# Direct Electrodeposition of Electrically Conducting Ni 3 (HITP) 2 MOF Nanostructures for Micro-Supercapacitor Integration

Sepideh Behboudikhiavi, Géraldine Chanteux, Binson Babu, Sébastien Faniel, Florent Marlec, Kevin Robert, Delphine Magnin, Fabio Lucaccioni, Joel Ojonugwa Omale, Petru Apostol, et al.

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To cite this version:

Sepideh Behboudikhiavi, Géraldine Chanteux, Binson Babu, Sébastien Faniel, Florent Marlec, et al. Direct Electrodeposition of Electrically Conducting Ni 3 (HITP) 2 MOF Nanostructures for Micro-Supercapacitor Integration. Small, 2024, 10.1002/smll.202401509. hal-04607931

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# Direct Electrodeposition of Electrically Conducting Ni 3 (HITP) 2 MOF Nanostructures for Micro-Supercapacitor Integration

Sepideh Behboudikhiavi, Géraldine Chanteux, Binson Babu, Sébastien Faniel, Florent Marlec, Kevin Robert, Delphine Magnin, Fabio Lucaccioni, Joel Ojonugwa Omale, Petru Apostol, et al.

► To cite this version:

Sepideh Behboudikhiavi, Géraldine Chanteux, Binson Babu, Sébastien Faniel, Florent Marlec, et al. Direct Electrodeposition of Electrically Conducting Ni 3 (HITP) 2 MOF Nanostructures for Micro-Supercapacitor Integration. Small, 2024, 10.1002/smll.202401509. hal-04607931

HAL Id: hal-04607931

https://hal.science/hal-04607931v1

Submitted on 17 Jun 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Direct Electrodeposition of Electrically Conducting Ni₃(HITP)₂ MOF Nanostructures for Micro-Supercapacitor Integration

Sepideh Behboudikhiavi[a]‡, Géraldine Chanteux[a]‡, Binson Babu[a], Sébastien Faniel[b], Florent Marlec[c,d], Kevin Robert[c,d], Delphine Magnin[a], Fabio Lucaccioni[a], Joel Ojonugwa Omale[a], Petru Apostol[a], Luc Piraux[a], Christophe Lethien[c,d,e], and Alexandru Vlad[a]*

A. Dr. S. Behboudikhiavi, G. Chanteux, Dr. B. Babu, Dr. D. Magnin, F. Lucaccioni, J. O. Omale, Dr. P. Apostol, Prof. L. Piraux, Prof. A. Vlad

Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain

1348, Louvain-la-Neuve, Belgium

E-mail: [alexandru.vlad@uclouvain.be](mailto:alexandru.vlad@uclouvain.be)

B. Dr. S. Faniel

Institute for Information and Communication Technologies, Electronics and Applied

Mathematics, Université catholique de Louvain

1348, Louvain-la-Neuve, Belgium

C. F. Marlec, K. Robert, Prof. C. Lethien

Institut d'Electronique, de Microélectronique et de Nanotechnologies, Université de Lille,

CNRS, Université Polytechnique Hauts-de-France, UMR 8520 – IEMN

59000, Lille, France

D. F. Marlec, K. Robert, Prof. C. Lethien

Réseau sur le Stockage Electrochimique de l'Energie (RS2E), CNRS FR 3459

33 rue Saint Leu

80039, Amiens Cedex, France

E. Prof. C. Lethien

Institut Universitaire de France (IUF),

Saint-Michel 103

75005, Paris, France

‡ Equal contribution
Direct Electrodeposition of Electrically Conducting Ni₃(HITP)₂ MOF Nanostructures for
Micro-Supercapacitor Integration

Sepideh Behboudikhiavi[a]‡, Géraldine Chanteux[a]‡, Binson Babu[a], Sébastien Faniel[b], Florent Marlec[c,d], Kevin Robert[c,d], Delphine Magnin[a], Fabio Lucaccioni[a], Joel Ojonugwa Omale[a], Petru Apostol[a], Luc Piraux[a], Christophe Lethien[c,d,e], and Alexandru Vlad[a]*

A. Dr. S. Behboudikhiavi, G. Chanteux, Dr. B. Babu, Dr. D. Magnin, F. Lucaccioni, J. O.

Omale, Dr. P. Apostol, Prof. L. Piraux, Prof. A. Vlad

Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain

1348, Louvain-la-Neuve, Belgium

E-mail: [alexandru.vlad@uclouvain.be](mailto:alexandru.vlad@uclouvain.be)

B. Dr. S. Faniel

Institute for Information and Communication Technologies, Electronics and Applied

Mathematics, Université catholique de Louvain

1348, Louvain-la-Neuve, Belgium

C. F. Marlec, K. Robert, Prof. C. Lethien

Institut d'Electronique, de Microélectronique et de Nanotechnologies, Université de Lille,

CNRS, Université Polytechnique Hauts-de-France, UMR 8520 – IEMN

59000, Lille, France

D. F. Marlec, K. Robert, Prof. C. Lethien

Réseau sur le Stockage Electrochimique de l'Energie (RS2E), CNRS FR 3459

33 rue Saint Leu

80039, Amiens Cedex, France

E. Prof. C. Lethien

Institut Universitaire de France (IUF),

Saint-Michel 103

75005, Paris, France

‡ Equal contribution
**Keywords:** non-sacrificial; anodic electrodeposition; micro-supercapacitor; MOFs
nanostructure

**Abstract:** Micro-supercapacitors emerge as an important electrical energy storage technology expected to play a critical role in the large-scale deployment of autonomous microdevices for health, sensing, monitoring, and other IoT applications. Electrochemical double-layer capacitive storage requires a combination of high surface area and high electronic conductivity, with these being attained only in porous or nanostructured carbons, and recently found also in conducting metal-organic frameworks. However, techniques for conformal deposition at micro- and nanoscale of these materials are complex, costly, and hard to upscale. Herein, we report direct, one step non-sacrificial anodic electrochemical deposition of Ni₃(2,3,6,7,10,11-hexaiminotriphenylene)₂ - Ni₃(HITP)₂, a porous and electrically conducting metal-organic framework. Employing this strategy enables the growth of Ni₃(HITP)₂ films on a variety of 2D substrates as well as on 3D nanostructured substrates to form Ni₃(HITP)₂ nanotubes and Pt@Ni₃(HITP)₂ core-shell nanowires. Based on the optimal electrodeposition protocols, Ni₃(HITP)₂ films interdigitated micro-supercapacitors are fabricated and tested as a proof of concept.

**Introduction**

Electrically conducting metal-organic frameworks (MOFs) are a class of materials of particular interest for energy storage applications requiring fast charging (i.e. electrochemical capacitor) due to their potential to attain high surface area exceeding 1.000 m².g⁻¹ and electrical conductivity up to 10³ S.cm⁻¹.[¹⁻⁵] Considering the increasing demand for wearable devices, microelectronics, and IoT applications, miniaturization of energy storage devices is essential, and micro-supercapacitors appear to be excellent candidates due to their high power density and long cycle lifetime.[⁶⁻⁹] However, the energy density remains low due to the limited double-layer capacitive storage mechanism as well as reduced size and low active material mass loading.[¹⁰⁻¹³] To improve the energy density, one of the strategies is to utilize pseudocapacitive materials such as conducting polymers[¹⁴,¹⁵], metal oxides[¹⁶⁻¹⁹], metal nitride[²⁰⁻²²], however at the expense of power density or cycling stability. Owing to the high conductivity, higher surface, and controllable porosity, conductive MOFs have emerged over the past years as excellent candidates for fabricating high-energy supercapacitors without compromising on power density
**Keywords:** non-sacrificial; anodic electrodeposition; micro-supercapacitor; MOFs
nanostructure

**Abstract:** Micro-supercapacitors emerge as an important electrical energy storage technology expected to play a critical role in the large-scale deployment of autonomous microdevices for health, sensing, monitoring, and other IoT applications. Electrochemical double-layer capacitive storage requires a combination of high surface area and high electronic conductivity, with these being attained only in porous or nanostructured carbons, and recently found also in conducting metal-organic frameworks. However, techniques for conformal deposition at micro- and nanoscale of these materials are complex, costly, and hard to upscale. Herein, we report direct, one step non-sacrificial anodic electrochemical deposition of Ni₃(2,3,6,7,10,11-hexaiminotriphenylene)₂ - Ni₃(HITP)₂, a porous and electrically conducting metal-organic framework. Employing this strategy enables the growth of Ni₃(HITP)₂ films on a variety of 2D substrates as well as on 3D nanostructured substrates to form Ni₃(HITP)₂ nanotubes and Pt@Ni₃(HITP)₂ core-shell nanowires. Based on the optimal electrodeposition protocols, Ni₃(HITP)₂ films interdigitated micro-supercapacitors are fabricated and tested as a proof of concept.

**Introduction**

Electrically conducting metal-organic frameworks (MOFs) are a class of materials of particular interest for energy storage applications requiring fast charging (i.e. electrochemical capacitor) due to their potential to attain high surface area exceeding 1.000 m².g⁻¹ and electrical conductivity up to 10³ S.cm⁻¹.[¹⁻⁵] Considering the increasing demand for wearable devices, microelectronics, and IoT applications, miniaturization of energy storage devices is essential, and micro-supercapacitors appear to be excellent candidates due to their high power density and long cycle lifetime.[⁶⁻⁹] However, the energy density remains low due to the limited double-layer capacitive storage mechanism as well as reduced size and low active material mass loading.[¹⁰⁻¹³] To improve the energy density, one of the strategies is to utilize pseudocapacitive materials such as conducting polymers[¹⁴,¹⁵], metal oxides[¹⁶⁻¹⁹], metal nitride[²⁰⁻²²], however at the expense of power density or cycling stability. Owing to the high conductivity, higher surface, and controllable porosity, conductive MOFs have emerged over the past years as excellent candidates for fabricating high-energy supercapacitors without compromising on power density
and cycling stability.[4,23] Hence, growing thin films of electrically conducting MOFs is considered as one key solution to tackle this challenge.[24–26]

However, conductive MOFs are typically synthesized in the form of polycrystalline or single-crystal bulk powder form, by means of various techniques such as diffusion (including mild and solvothermal conditions), microwave assisted, mechanochemical, and electrochemical methods.[27] Given the bulk nature of nucleation and growth process, these conventional methods are difficult to adapt for the preparation of controlled nanostructures, or conformal and selected area thin film coating. A significant effort has thus been devoted to elaborating on various techniques for film growth or integration of conducting (as well as non-conducting) MOFs on solid substrates. These include exfoliation and reassembly[28], liquid phase epitaxy[29], gas-liquid phase interfacial[3,30], Langmuir-Blodgett layer-by-layer deposition[31], chemical vapor deposition[32,33], electrochemical synthesis[34], and electrodeposition[24–26]. However, except for electrodeposition, these techniques are time and resource consuming deriving from the lack of precise controllability of growth kinetics and low reproducibility. Additionally, some methods cannot be applied to certain classes of MOF, given the requirements of the deposition methods (e.g. volatile precursors, thermal or chemical stability).

Electrochemical deposition is a well-established thin film growth method, that has been extensively researched over the past century and is now firmly consolidated in industrial processes such as refining, electro-winning, and electroplating. A variety of materials can be synthesized by electrodeposition, for instance, metals, alloys, polymers, oxides; with also various morphologies, like thin film, nanoparticles, nanorods and nanowires, etc.[35] Electrochemical deposition critically enables well-tuned and large-area conformal thin films coatings of various insulating or conducting films on versatile conducting substrates with complex geometries.[18,19,24,36] The method can be conducted in mild conditions thus allowing the deposition of conformal and uniform films with various morphologies through adjustment of the parameters of electrodeposition.[27,37–39]

The MOF electrodeposition techniques can be divided into cathodic or anodic processes. The former[40] has been dominantly employed to produce thin films of non-conductive MOFs, for instance, Zn₄O(BDC)₃[41,42] and Cu-BTC[43]. The underlying mechanism relies on the electrochemical reduction of sacrificial chemical species (pro bases) such as NO₃⁻ and H₂O₂, generating OH⁻ to deprotonate the linker, resulting in MOF chemical deposition on the cathode surface. The cathodic deposition has been largely applied for the synthesis of non-conductive MOFs, and only few reports describing the cathodic deposition of Cu catecholate conducting MOFs can be found.[44] In comparison, the anodic deposition proved to be more versatile and
and cycling stability.[4,23] Hence, growing thin films of electrically conducting MOFs is considered as one key solution to tackle this challenge.[24–26]

However, conductive MOFs are typically synthesized in the form of polycrystalline or single-crystal bulk powder form, by means of various techniques such as diffusion (including mild and solvothermal conditions), microwave assisted, mechanochemical, and electrochemical methods.[27] Given the bulk nature of nucleation and growth process, these conventional methods are difficult to adapt for the preparation of controlled nanostructures, or conformal and selected area thin film coating. A significant effort has thus been devoted to elaborating on various techniques for film growth or integration of conducting (as well as non-conducting) MOFs on solid substrates. These include exfoliation and reassembly[28], liquid phase epitaxy[29], gas-liquid phase interfacial[3,30], Langmuir-Blodgett layer-by-layer deposition[31], chemical vapor deposition[32,33], electrochemical synthesis[34], and electrodeposition[24–26]. However, except for electrodeposition, these techniques are time and resource consuming deriving from the lack of precise controllability of growth kinetics and low reproducibility. Additionally, some methods cannot be applied to certain classes of MOF, given the requirements of the deposition methods (e.g. volatile precursors, thermal or chemical stability).

Electrochemical deposition is a well-established thin film growth method, that has been extensively researched over the past century and is now firmly consolidated in industrial processes such as refining, electro-winning, and electroplating. A variety of materials can be synthesized by electrodeposition, for instance, metals, alloys, polymers, oxides; with also various morphologies, like thin film, nanoparticles, nanorods and nanowires, etc.[35] Electrochemical deposition critically enables well-tuned and large-area conformal thin films coatings of various insulating or conducting films on versatile conducting substrates with complex geometries.[18,19,24,36] The method can be conducted in mild conditions thus allowing the deposition of conformal and uniform films with various morphologies through adjustment of the parameters of electrodeposition.[27,37–39]

The MOF electrodeposition techniques can be divided into cathodic or anodic processes. The former[40] has been dominantly employed to produce thin films of non-conductive MOFs, for instance, Zn₄O(BDC)₃[41,42] and Cu-BTC[43]. The underlying mechanism relies on the electrochemical reduction of sacrificial chemical species (pro bases) such as NO₃⁻ and H₂O₂, generating OH⁻ to deprotonate the linker, resulting in MOF chemical deposition on the cathode surface. The cathodic deposition has been largely applied for the synthesis of non-conductive MOFs, and only few reports describing the cathodic deposition of Cu catecholate conducting MOFs can be found.[44] In comparison, the anodic deposition proved to be more versatile and
has been applied for the synthesis of both, insulating and conducting MOF films.[45-50] However, both methods as specifically applied to MOF growth have a series of technical and practical intrinsic limitations. For instance, metallic impurities may be incorporated into the MOF by either electrochemical reduction of metal ions (in the cathodic process) or from remaining domains of the sacrificed metallic anode (in the anodic process).[42] Controlled deposition of MOF nanostructures (nanowires, nanotubes inside a template for example), or functionalization of nanostructured metal films (e.g. core-shell nanowires or simply growth on patterned metallic micro- or nano-electrodes) remains scarcely feasible given the particular conditions used in the developed approaches. Therefore, the challenge is to elaborate a non-sacrificial method to obtain highly pure conductive MOF films on 2D and 3D substrates.

Worth being mentioned also the mechanism particularities of these methods. The conventional anodic deposition of MOF is based on first step anodic generation of metal cations (by corrosion from the working substrate electrode) in an electrolytic bath containing the ligand and specific additives (Scheme 1A). Metal cations then diffuse and react with linker to yield the MOF. This process however decouples the intrinsic electron conducting property of a conducting MOF from the electrodeposition charge transfer step and interface. In fact, these will take place at the metal electrode – electrolyte interface (Scheme 1B),[51] with the MOF growth however proceeding at the MOF-electrolyte interface, by the metal cation diffusion. This is partially counterintuitive, as one would expect that charge transfer and material growth to take place at the same interface, as it is the case for all previously deposited conducting materials (e.g. metals, semiconductors, conducting polymers). Surprising as it may sound, direct and non-sacrificial electrochemical deposition of conducting MOFs thus far has little benefited from this intrinsic property.

Here, we report a one-step, non-sacrificial anodic electrochemical deposition of Ni₃(2,3,6,7,10,11-hexaiminotriphenylene)₂ electronically conducting MOF (Scheme 1A). The spontaneous oxidation of the ligand step, attributed to the molecular oxygen from air is replaced by a controlled electrochemical oxidation (under Argon atmosphere) of the ligand. A precise control over electrochemical parameters was required to ensure the growth of Ni₃(HITP)₂ films with targeted thickness. The electrochemical behaviour of all chemical species present in the air-free electrolytic bath were first analysed separately and then combined all together to understand the redox activities. Based on the analysis of the electrolytic bath components, the non-sacrificial anodic deposition of Ni₃(HITP)₂ was then optimized in an air-free electrolytic bath in both aqueous-based (H₂O-DMF-DMA) and organic (MeOH-DMSO) electrolytic solutions. The thickness, morphology, and phase purity of the films are tuneable by the
has been applied for the synthesis of both, insulating and conducting MOF films.[45-50] However, both methods as specifically applied to MOF growth have a series of technical and practical intrinsic limitations. For instance, metallic impurities may be incorporated into the MOF by either electrochemical reduction of metal ions (in the cathodic process) or from remaining domains of the sacrificed metallic anode (in the anodic process).[42] Controlled deposition of MOF nanostructures (nanowires, nanotubes inside a template for example), or functionalization of nanostructured metal films (e.g. core-shell nanowires or simply growth on patterned metallic micro- or nano-electrodes) remains scarcely feasible given the particular conditions used in the developed approaches. Therefore, the challenge is to elaborate a non-sacrificial method to obtain highly pure conductive MOF films on 2D and 3D substrates.

Worth being mentioned also the mechanism particularities of these methods. The conventional anodic deposition of MOF is based on first step anodic generation of metal cations (by corrosion from the working substrate electrode) in an electrolytic bath containing the ligand and specific additives (Scheme 1A). Metal cations then diffuse and react with linker to yield the MOF. This process however decouples the intrinsic electron conducting property of a conducting MOF from the electrodeposition charge transfer step and interface. In fact, these will take place at the metal electrode – electrolyte interface (Scheme 1B),[51] with the MOF growth however proceeding at the MOF-electrolyte interface, by the metal cation diffusion. This is partially counterintuitive, as one would expect that charge transfer and material growth to take place at the same interface, as it is the case for all previously deposited conducting materials (e.g. metals, semiconductors, conducting polymers). Surprising as it may sound, direct and non-sacrificial electrochemical deposition of conducting MOFs thus far has little benefited from this intrinsic property.

Here, we report a one-step, non-sacrificial anodic electrochemical deposition of Ni₃(2,3,6,7,10,11-hexaiminotriphenylene)₂ electronically conducting MOF (Scheme 1A). The spontaneous oxidation of the ligand step, attributed to the molecular oxygen from air is replaced by a controlled electrochemical oxidation (under Argon atmosphere) of the ligand. A precise control over electrochemical parameters was required to ensure the growth of Ni₃(HITP)₂ films with targeted thickness. The electrochemical behaviour of all chemical species present in the air-free electrolytic bath were first analysed separately and then combined all together to understand the redox activities. Based on the analysis of the electrolytic bath components, the non-sacrificial anodic deposition of Ni₃(HITP)₂ was then optimized in an air-free electrolytic bath in both aqueous-based (H₂O-DMF-DMA) and organic (MeOH-DMSO) electrolytic solutions. The thickness, morphology, and phase purity of the films are tuneable by the
deposition parameters such as pulsed, continuous potentiostatic, or potentiodynamic (CV) conditions, the maximal amount of applied charge, the chemical composition of the electrolytic bath, and the deposition time. The optimization of different parameters enabled the deposition of Ni₃(HITP)₂ thin films on various conductive substrates (metals, carbon semiconductors) of different geometries leading to different morphologies of the Ni₃(HITP)₂ films (planar surfaces, nanowire, nanotube and porous networks, core-shell architectures and interdigitated structures). Finally, the deposition method was integrated as a facile pragmatic technique to fabricate micro-supercapacitors based on Ni₃(HITP)₂ functionalized interdigitated electrodes with high areal capacitance and long-term cycling stability. To be mentioned, in the final stage of preparation of this work, a complementary development was reported by Lu et al [52], wherein anodic electrochemical-chemical deposition of catecholate-based MOF in aqueous electrolytic bath was realized on various substrates and of nanostructures. Our work extends the applicability to amine-based MOF in both aqueous-based and organic electrolytic bath, with micro-supercapacitor device integration, with both developments thus validating and consolidating the universality of non-sacrificial anodic electrodeposition of electrically conducting MOFs.

<figure><img src="image_3.png" /><figcaption>**Scheme 1.** Schematics of (A) the anodic sacrificial electrodeposition with (B) the corresponding growth mechanism with decoupled charge transfer and reaction interfaces, as compared to (C) direct non-sacrificial electrochemical deposition method for Ni₃(HITP)₂ applied in this work and the corresponding (D) growth mechanism at the interface.</figcaption></figure>

**Results and discussion**
deposition parameters such as pulsed, continuous potentiostatic, or potentiodynamic (CV) conditions, the maximal amount of applied charge, the chemical composition of the electrolytic bath, and the deposition time. The optimization of different parameters enabled the deposition of Ni₃(HITP)₂ thin films on various conductive substrates (metals, carbon semiconductors) of different geometries leading to different morphologies of the Ni₃(HITP)₂ films (planar surfaces, nanowire, nanotube and porous networks, core-shell architectures and interdigitated structures). Finally, the deposition method was integrated as a facile pragmatic technique to fabricate micro-supercapacitors based on Ni₃(HITP)₂ functionalized interdigitated electrodes with high areal capacitance and long-term cycling stability. To be mentioned, in the final stage of preparation of this work, a complementary development was reported by Lu et al [52], wherein anodic electrochemical-chemical deposition of catecholate-based MOF in aqueous electrolytic bath was realized on various substrates and of nanostructures. Our work extends the applicability to amine-based MOF in both aqueous-based and organic electrolytic bath, with micro-supercapacitor device integration, with both developments thus validating and consolidating the universality of non-sacrificial anodic electrodeposition of electrically conducting MOFs.

<figure><img src="image_2.png" /><figcaption>**Scheme 1.** Schematics of (A) the anodic sacrificial electrodeposition with (B) the corresponding growth mechanism with decoupled charge transfer and reaction interfaces, as compared to (C) direct non-sacrificial electrochemical deposition method for Ni₃(HITP)₂ applied in this work and the corresponding (D) growth mechanism at the interface.</figcaption></figure>

**Results and discussion**
The anodic electrodeposition procedure for Ni₃(HITP)₂ is schematized in Scheme 1C. The electrodeposition of Ni₃(HITP)₂ from an electrolytic bath including all precursors (i.e. HATP ligand, base, and Ni²⁺ ions) can mitigate all the challenges related to the sacrificial anodic dissolution of metallic Ni film as the source of metallic cations. The growth and charge transfer thus simultaneously take place at the MOF electrode - electrolyte interface (Scheme 1D). Accordingly, this method is expected to entail the local generation of electrochemically oxidized HATP ligand through charge transfer interface, followed by the formation of Ni₃(HITP)₂ film at the exact same interface, as it is the case for conventional electrodeposition of conducting materials (e.g. metals, semiconductors, conducting polymers).

The challenging feature in the electrodeposition of Ni₃(HITP)₂ is that the reactant mixture, or the electrolytic bath, is not stable under ambient air conditions. In fact, the molecular oxygen (O₂) is a co-reactant in the Ni₃(HITP)₂ formation reaction, by oxidizing the deprotonated HATP ligand. Subsequently, the oxidized ligand undergoes a series of reactions implying Ni²⁺ coordination and acid-base reactions, to form the Ni₃(HITP)₂ MOF with diiminobenzosemiquinoate submoieties, following one of the three reaction pathways displayed in Figure 1A (essentially depending on the composition of the electrolytic bath - amount of Ni²⁺, HATP and basic species).[53-56] Thus, our rationale was to eliminate the molecular oxygen from the electrolytic bath, and activate this initial anodic step electrochemically (Figure 1A). To attest this, the lower coordination ability of the (diamino)₂-Ni, relative to the (diimino)₂-Ni moieties, was first elucidated. For instance, all constituents including HATP.6HCl, Ni²⁺ and a large excess of NaOAc were added to a deaerated H₂O-DMF-DMA mixed solvent.[57] Upon heating at 80 °C and keeping the reaction mixture under inert atmosphere, no reaction took place and the electrolytic bath remained unchanged for more than 2 hours (Figure S1-A). On the contrary, the formation of Ni₃(HITP)₂ was promptly discerned upon exposing the mixture to ambient air conditions (i.e. O₂ diffusion and reaction, Figure S1-B).

Next, a series of control experiments were performed to elucidate the role of individual electrolytic bath constituents (Figure 1B). In an electrolyte comprising only Ni²⁺ salt, no redox process was observed within the studied potential window from -0.5 up to 1.0 V (vs. Ag pseudo-reference), consistent with the anodic stability of Ni²⁺. Instead, HATP manifested a sharp anodic process at ~ 0.3V vs. Ag, representative of the redox of similar *o*-benzenediamine species,[58,59] and consistent with the theoretical potential of ~0.30V. The low anodic stability of deprotonated HATP in solution is also in agreement with its reactivity towards molecular O₂.

The tail on the anodic wave can be explained by the subsequent formation of complex species, potentially arising from the supramolecular packing of the oxidized deprotonated ligand
The anodic electrodeposition procedure for Ni₃(HITP)₂ is schematized in Scheme 1C. The electrodeposition of Ni₃(HITP)₂ from an electrolytic bath including all precursors (i.e. HATP ligand, base, and Ni²⁺ ions) can mitigate all the challenges related to the sacrificial anodic dissolution of metallic Ni film as the source of metallic cations. The growth and charge transfer thus simultaneously take place at the MOF electrode - electrolyte interface (Scheme 1D). Accordingly, this method is expected to entail the local generation of electrochemically oxidized HATP ligand through charge transfer interface, followed by the formation of Ni₃(HITP)₂ film at the exact same interface, as it is the case for conventional electrodeposition of conducting materials (e.g. metals, semiconductors, conducting polymers).

The challenging feature in the electrodeposition of Ni₃(HITP)₂ is that the reactant mixture, or the electrolytic bath, is not stable under ambient air conditions. In fact, the molecular oxygen (O₂) is a co-reactant in the Ni₃(HITP)₂ formation reaction, by oxidizing the deprotonated HATP ligand. Subsequently, the oxidized ligand undergoes a series of reactions implying Ni²⁺ coordination and acid-base reactions, to form the Ni₃(HITP)₂ MOF with diiminobenzosemiquinoate submoieties, following one of the three reaction pathways displayed in Figure 1A (essentially depending on the composition of the electrolytic bath - amount of Ni²⁺, HATP and basic species).[53-56] Thus, our rationale was to eliminate the molecular oxygen from the electrolytic bath, and activate this initial anodic step electrochemically (Figure 1A). To attest this, the lower coordination ability of the (diamino)₂-Ni, relative to the (diimino)₂-Ni moieties, was first elucidated. For instance, all constituents including HATP.6HCl, Ni²⁺ and a large excess of NaOAc were added to a deaerated H₂O-DMF-DMA mixed solvent.[57] Upon heating at 80 °C and keeping the reaction mixture under inert atmosphere, no reaction took place and the electrolytic bath remained unchanged for more than 2 hours (Figure S1-A). On the contrary, the formation of Ni₃(HITP)₂ was promptly discerned upon exposing the mixture to ambient air conditions (i.e. O₂ diffusion and reaction, Figure S1-B).

Next, a series of control experiments were performed to elucidate the role of individual electrolytic bath constituents (Figure 1B). In an electrolyte comprising only Ni²⁺ salt, no redox process was observed within the studied potential window from -0.5 up to 1.0 V (vs. Ag pseudo-reference), consistent with the anodic stability of Ni²⁺. Instead, HATP manifested a sharp anodic process at ~ 0.3V vs. Ag, representative of the redox of similar *o*-benzenediamine species,[58,59] and consistent with the theoretical potential of ~0.30V. The low anodic stability of deprotonated HATP in solution is also in agreement with its reactivity towards molecular O₂.

The tail on the anodic wave can be explained by the subsequent formation of complex species, potentially arising from the supramolecular packing of the oxidized deprotonated ligand
(through π-π stacking, that could supposedly form rigid molecular columns)[60] and more likely *via* aromatization and polymerization chain reactions (resulting in phenazine or 1,4-benzoquinone-diimine - type polymers). The process is irreversible as no associated cathodic process could be observed. This is explained by the basic conditions (pH ~9) of the electrolytic bath, wherein the oxidized HATP and HATP participate in chemical reactions (dimerization and polymerization).[58]

<figure><img src="image_4.png" /><figcaption>**Figure 1.** (A) The mechanism of Ni₃(HITP)₂ synthesis implying initial HATP ligand chemical or electrochemical oxidation, followed by a series of acid-base and coordination reactions. (B) Cyclic voltammograms of individually containing Ni(OAc)₂ and HATP solutions, as compared to the Ni₃(HITP)₂ precursors electrolytic bath, all acquired at a scan rate of 10 mV·s⁻¹ on ITO working electrode.</figcaption></figure>

In presence of both components, HATP and Ni(OAc)₂, the anodic peak is broadening, concomitant with an earlier onset of oxidation and an associated reduction peak at ~ -0.05V vs Ag in the reverse scan (Figure 1B). The oxidation onset at 0.05V is interpreted as the oxidation of HATP, facilitated (i.e. stabilized) by the subsequent coordination reaction with Ni²⁺. The anodic peak broadening is attributed to the emergence and deposition of more intricate entities, such as coordinated Ni²⁺ ions with the oxidized hexaiminotriphenylene (small and long chain Ni₃(HITP)₂ species) or ligand-based polymers, processes dependent on HATP oxidation conditions and Ni²⁺ coordination kinetics.[58] The reduction peak in the reverse scan is associated to the reduction of the formed and oxidized species, including redox of Ni₃(HITP)₂ (as afterwards exploited for pseudocapacitive storage, see discussion and results in next sections). A comparable electrochemical behaviour was previously observed by Pelmus *et al.* for the 1,4-diaminobenzene organic compound.[59] To be noted that already after the first cyclic
(through π-π stacking, that could supposedly form rigid molecular columns)[60] and more likely *via* aromatization and polymerization chain reactions (resulting in phenazine or 1,4-benzoquinone-diimine - type polymers). The process is irreversible as no associated cathodic process could be observed. This is explained by the basic conditions (pH ~9) of the electrolytic bath, wherein the oxidized HATP and HATP participate in chemical reactions (dimerization and polymerization).[58]

<figure><img src="image_3.png" /><figcaption>**Figure 1.** (A) The mechanism of Ni₃(HITP)₂ synthesis implying initial HATP ligand chemical or electrochemical oxidation, followed by a series of acid-base and coordination reactions. (B) Cyclic voltammograms of individually containing Ni(OAc)₂ and HATP solutions, as compared to the Ni₃(HITP)₂ precursors electrolytic bath, all acquired at a scan rate of 10 mV·s⁻¹ on ITO working electrode.</figcaption></figure>

In presence of both components, HATP and Ni(OAc)₂, the anodic peak is broadening, concomitant with an earlier onset of oxidation and an associated reduction peak at ~ -0.05V vs Ag in the reverse scan (Figure 1B). The oxidation onset at 0.05V is interpreted as the oxidation of HATP, facilitated (i.e. stabilized) by the subsequent coordination reaction with Ni²⁺. The anodic peak broadening is attributed to the emergence and deposition of more intricate entities, such as coordinated Ni²⁺ ions with the oxidized hexaiminotriphenylene (small and long chain Ni₃(HITP)₂ species) or ligand-based polymers, processes dependent on HATP oxidation conditions and Ni²⁺ coordination kinetics.[58] The reduction peak in the reverse scan is associated to the reduction of the formed and oxidized species, including redox of Ni₃(HITP)₂ (as afterwards exploited for pseudocapacitive storage, see discussion and results in next sections). A comparable electrochemical behaviour was previously observed by Pelmus *et al.* for the 1,4-diaminobenzene organic compound.[59] To be noted that already after the first cyclic
voltammetry (CV) scan, a thin film of dark blue translucent reflection covered the working electrode surface, corresponding to the Ni₃(HITP)₂ deposits confirming the charge passed during the electrodeposition process (Figure S2-A).

Methods and conditions were next optimized to establish the optimal deposition parameters. Both cyclic voltammetry and potentiostatic (continuous or pulsed potential) electrodeposition techniques were selected and tested. In the cyclic voltammograms using the MeOH-DMSO electrolytic bath (Figure 2A), a gradual reduction of the anodic current was accompanied by a peak shifting towards higher potentials. This is explained by the progressive nucleation and growth of the less conductive Ni₃(HITP)₂ on the surface of ITO,[61] resulting in partial surface passivation, decreased current density and increased polarization, as also confirmed by SEM analysis of the ITO surface after individual CV scans (Figure 2B). Regarding the top surface SEM imaging, a Volmer-Verbeer island growth mode seems to be involved in the electrodeposition process of MOF.[62] After several CV cycles (typically more than 10), the anodic electrodeposition current became low indicating a self-limiting growth, consistent with the observations on benzene-1,4-diamine electrochemical studies by Pelmus et al.[59] Constant potential anodic electrodeposition was also studied. Both, aqueous based (H₂O-DMA-DMF) and organic (MeOH-DMSO) electrolytic baths were tested. First, a wide potential window was applied, in accordance with cyclic voltammograms for each specific condition (Figure S3). The potentiostatic deposition (in H₂O-DMA-DMF) at 0.5 V provided the most crystalline and uniform film as corroborated by XRD analysis (Figures 3 and S4-A). Chronoamperograms for continuous and pulsed potentiostatic depositions are shown in Figure 2C. For the continuous deposition method, a rapid drop of the current density was noted, corroborating the CV analysis (Figure 1B) of gradual passivation of the surface, but also possibly originating from reactants diffusion limited process. The pulsed method manifested in turn a lower current density drop and a higher charge density on average, by allowing diffusion and replenishment of the electroactive species in the diffusion layer.
voltammetry (CV) scan, a thin film of dark blue translucent reflection covered the working electrode surface, corresponding to the Ni₃(HITP)₂ deposits confirming the charge passed during the electrodeposition process (Figure S2-A).

Methods and conditions were next optimized to establish the optimal deposition parameters. Both cyclic voltammetry and potentiostatic (continuous or pulsed potential) electrodeposition techniques were selected and tested. In the cyclic voltammograms using the MeOH-DMSO electrolytic bath (Figure 2A), a gradual reduction of the anodic current was accompanied by a peak shifting towards higher potentials. This is explained by the progressive nucleation and growth of the less conductive Ni₃(HITP)₂ on the surface of ITO,[61] resulting in partial surface passivation, decreased current density and increased polarization, as also confirmed by SEM analysis of the ITO surface after individual CV scans (Figure 2B). Regarding the top surface SEM imaging, a Volmer-Verbeer island growth mode seems to be involved in the electrodeposition process of MOF.[62] After several CV cycles (typically more than 10), the anodic electrodeposition current became low indicating a self-limiting growth, consistent with the observations on benzene-1,4-diamine electrochemical studies by Pelmus et al.[59] Constant potential anodic electrodeposition was also studied. Both, aqueous based (H₂O-DMA-DMF) and organic (MeOH-DMSO) electrolytic baths were tested. First, a wide potential window was applied, in accordance with cyclic voltammograms for each specific condition (Figure S3). The potentiostatic deposition (in H₂O-DMA-DMF) at 0.5 V provided the most crystalline and uniform film as corroborated by XRD analysis (Figures 3 and S4-A). Chronoamperograms for continuous and pulsed potentiostatic depositions are shown in Figure 2C. For the continuous deposition method, a rapid drop of the current density was noted, corroborating the CV analysis (Figure 1B) of gradual passivation of the surface, but also possibly originating from reactants diffusion limited process. The pulsed method manifested in turn a lower current density drop and a higher charge density on average, by allowing diffusion and replenishment of the electroactive species in the diffusion layer.
<figure><img src="image_5.png" /><figcaption>B</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>C</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>D</figcaption></figure>

<figure><img src="image_8.png" /></figure>

**Figure 2.** (A) Cyclic voltammograms using the organic-based (MeOH-DMSO) electrolytic bath recorded at a scan rate of 10 mV·s⁻¹ on ITO substrate. (B) The SEM images of Ni₃(HITP)₂ deposits on ITO surface after selected cyclic voltammetry scans. (C) The chronoamperograms (normalized current density) and the corresponding cumulative deposition charge density for potentiostatic anodic deposition methods by using the continuous (dark colored line) and square pulsed (light colored line) methods (with t_on = 1 min, V_on = 0.8 V; and t_off = 1 min, V_off = open circuit voltage). (D) The corresponding SEM images of Ni₃(HITP)₂ deposits obtained by potentiostatic continuous (dark colored contour) and pulsed deposition (light colored contour).

In MeOH-DMSO electrolytic bath, continuous deposition of Ni₃(HITP)₂ resulted in a needle-shaped spherical aggregated crystalline film morphology, whereas pulsed deposition yielded a smoother spherical-based crystalline deposit (Figure 2D). The crystallites size is notably higher under continuous deposition. The opposite situation (i.e. smaller size of crystallites) is observed for pulsed deposition, which can be explained by limited growth and augmented nucleation and diffusion rate due to the application of t_off. Indeed, pulsed deposition exhibited different morphologies resulting in a more uniform film, with finer grains when $\frac{t_{on}}{t_{on}+t_{off}}$ factor was smaller – with t_on from 1 min to 100 ms and t_off from 1 min to 10 sec, respectively (Figure S5-
A

<figure><img src="image_4.png" /></figure>

B

<figure><img src="image_5.png" /></figure>

C

<figure><img src="image_6.png" /></figure>

D

<figure><img src="image_7.png" /></figure>

**Figure 2.** (A) Cyclic voltammograms using the organic-based (MeOH-DMSO) electrolytic bath recorded at a scan rate of 10 mV·s⁻¹ on ITO substrate. (B) The SEM images of Ni₃(HITP)₂ deposits on ITO surface after selected cyclic voltammetry scans. (C) The chronoamperograms (normalized current density) and the corresponding cumulative deposition charge density for potentiostatic anodic deposition methods by using the continuous (dark colored line) and square pulsed (light colored line) methods (with t_on = 1 min, V_on = 0.8 V; and t_off = 1 min, V_off = open circuit voltage). (D) The corresponding SEM images of Ni₃(HITP)₂ deposits obtained by potentiostatic continuous (dark colored contour) and pulsed deposition (light colored contour).

In MeOH-DMSO electrolytic bath, continuous deposition of Ni₃(HITP)₂ resulted in a needle-shaped spherical aggregated crystalline film morphology, whereas pulsed deposition yielded a smoother spherical-based crystalline deposit (Figure 2D). The crystallites size is notably higher under continuous deposition. The opposite situation (i.e. smaller size of crystallites) is observed for pulsed deposition, which can be explained by limited growth and augmented nucleation and diffusion rate due to the application of t_off. Indeed, pulsed deposition exhibited different morphologies resulting in a more uniform film, with finer grains when $\frac{t_{on}}{t_{on}+t_{off}}$ factor was smaller – with t_on from 1 min to 100 ms and t_off from 1 min to 10 sec, respectively (Figure S5-
C and D).[63,64] In contrast, continuous potentiostatic deposition of Ni₃(HITP)₂ using the H₂O-DMF-DMA electrolytic bath displayed bigger lamellar spherical aggregates, with nuclei proliferating on the surface (Figure S5-A and B).

ATR-IR spectroscopy analysis indicated that films obtained by electrochemical deposition method, in both H₂O-DMF-DMA and MeOH-DMSO electrolytic baths, possess the typical signature of Ni₃(HITP)₂ bands, particularly with the aromatic bands in the 1200 – 1500 cm⁻¹ region (Figure S6). No signatures of unreacted ligand could be detected. The X-Ray Diffraction analysis on powder (PXRD) revealed that among all methods evaluated, the most crystallized MOF films were achieved under potentiostatic conditions using the H₂O-DMF-DMA electrolytic bath, or pulsed potentiostatic conditions using the MeOH-DMSO electrolytic bath (Figure 3). All the Bragg peaks were assigned to simulated and bulk chemically synthesized Ni₃(HITP)₂ phase (Figure 3A-B) are clearly defined for the films obtained *via* potentiostatic (continuous and pulsed) deposition methods (Figure 3D-F).[56] The PXRD of the material prepared by potentiodynamic method did not provide any discernible crystalline phase, whereas the crystallinity of deposits derived from potentiostatic continuous deposition could be enhanced *via* pulsed deposition (Figure 3D-F). The main reasons of such differences can be explained by the lack of oxidation control as well as charge/mass transfer kinetics of the electroactive species (leading to different oxidation levels/states) under potentiodynamic deposition and species’ diffusion limitations under continuous potentiostatic deposition. Accordingly, the pulsed potentiostatic deposition in MeOH-DMSO electrolytic bath was selected as the most appropriate method for further studies and device integration. No other diffraction peaks could be as well identified in the PXRD of deposits. To further prove the composition and purity of the electrodeposited Ni₃(HITP)₂, XPS analysis was conducted (Figure S7). The peaks in the high resolution spectrum of Ni2p (Ni2p1/2 at 854.79 eV and Ni2p3/2 at 872.38 eV) are exclusively assigned to Ni²⁺ in pure Ni₃(HITP)₂ without any trace of other possible parasitic species (i.e. Ni0, Ni(OH)₂ or NiO).
C and D).[63,64] In contrast, continuous potentiostatic deposition of Ni₃(HITP)₂ using the H₂O-DMF-DMA electrolytic bath displayed bigger lamellar spherical aggregates, with nuclei proliferating on the surface (Figure S5-A and B).

ATR-IR spectroscopy analysis indicated that films obtained by electrochemical deposition method, in both H₂O-DMF-DMA and MeOH-DMSO electrolytic baths, possess the typical signature of Ni₃(HITP)₂ bands, particularly with the aromatic bands in the 1200 – 1500 cm⁻¹ region (Figure S6). No signatures of unreacted ligand could be detected. The X-Ray Diffraction analysis on powder (PXRD) revealed that among all methods evaluated, the most crystallized MOF films were achieved under potentiostatic conditions using the H₂O-DMF-DMA electrolytic bath, or pulsed potentiostatic conditions using the MeOH-DMSO electrolytic bath (Figure 3). All the Bragg peaks were assigned to simulated and bulk chemically synthesized Ni₃(HITP)₂ phase (Figure 3A-B) are clearly defined for the films obtained *via* potentiostatic (continuous and pulsed) deposition methods (Figure 3D-F).[56] The PXRD of the material prepared by potentiodynamic method did not provide any discernible crystalline phase, whereas the crystallinity of deposits derived from potentiostatic continuous deposition could be enhanced *via* pulsed deposition (Figure 3D-F). The main reasons of such differences can be explained by the lack of oxidation control as well as charge/mass transfer kinetics of the electroactive species (leading to different oxidation levels/states) under potentiodynamic deposition and species’ diffusion limitations under continuous potentiostatic deposition. Accordingly, the pulsed potentiostatic deposition in MeOH-DMSO electrolytic bath was selected as the most appropriate method for further studies and device integration. No other diffraction peaks could be as well identified in the PXRD of deposits. To further prove the composition and purity of the electrodeposited Ni₃(HITP)₂, XPS analysis was conducted (Figure S7). The peaks in the high resolution spectrum of Ni2p (Ni2p1/2 at 854.79 eV and Ni2p3/2 at 872.38 eV) are exclusively assigned to Ni²⁺ in pure Ni₃(HITP)₂ without any trace of other possible parasitic species (i.e. Ni0, Ni(OH)₂ or NiO).
<figure><img src="image_9.png" /><figcaption>**Figure 3.** (A) Simulated and (B) experimental PXRD pattern of Ni₃(HITP)₂ made by chemical synthesis. PXRD patterns of Ni₃(HITP)₂ deposits obtained by (C) potentiodynamic deposition in MeOH-DMSO electrolytic bath, (D) potentiostatic deposition in H₂O-DMF-DMA electrolytic bath, (E) continuous and (F) pulsed potentiostatic deposition in MeOH-DMSO electrolytic bath.</figcaption></figure>

The compatibility of the anodic deposition of MOF films on various substrates is a key aspect for advances in microdevice integration. To this end, four additional conductive substrates - Pt sheet, stainless steel sheet, vanadium-nitride coated on Si/Si₃N₄ sample and carbon cloth - were tested as working current collectors for the electrodeposition of Ni₃(HITP)₂ films using the optimized pulsed potentiostatic method in MeOH-DMSO electrolytic bath (Figure 4). SEM analyses revealed analogous spherical aggregates morphologies on all tested substrates, echoing the resultant deposited films on ITO substrate. Specifically, the Ni₃(HITP)₂ deposition on vanadium-nitride current collectors appeared as a homogeneous film, punctuated by very small spherical particles smaller than 200 nm in diameter. Comparatively, the Ni₃(HITP)₂ deposits on other substrates are formed of bigger spherical aggregated particles, of dimensions ranging from 200 to 300 nm in diameter on carbon cloth, expanding to 1 µm diameter on stainless-steel sheet, and reaching more than 2-3 µm diameter on Pt sheet. These discrepancy in film morphology and particles diameter can be attributed to the roughness, wettability and electrocatalytic effect of each current collector, which modulate the nuclei growth and kinetics, thus dictating the texture of the Ni₃(HITP)₂ films.[65]
<figure><img src="image_8.png" /><figcaption>**Figure 3.** (A) Simulated and (B) experimental PXRD pattern of Ni₃(HITP)₂ made by chemical synthesis. PXRD patterns of Ni₃(HITP)₂ deposits obtained by (C) potentiodynamic deposition in MeOH-DMSO electrolytic bath, (D) potentiostatic deposition in H₂O-DMF-DMA electrolytic bath, (E) continuous and (F) pulsed potentiostatic deposition in MeOH-DMSO electrolytic bath.</figcaption></figure>

The compatibility of the anodic deposition of MOF films on various substrates is a key aspect for advances microdevice integration. To this end, four additional conductive substrates - Pt sheet, stainless steel sheet, vanadium-nitride coated on Si/Si₃N₄ sample and carbon cloth - were tested as working current collectors for the electrodeposition of Ni₃(HITP)₂ films using the optimized pulsed potentiostatic method in MeOH-DMSO electrolytic bath (Figure 4). SEM analyses revealed analogous spherical aggregates morphologies on all tested substrates, echoing the resultant deposited films on ITO substrate. Specifically, the Ni₃(HITP)₂ deposition on vanadium-nitride current collectors appeared as a homogeneous film, punctuated by very small spherical particles smaller than 200 nm in diameter. Comparatively, the Ni₃(HITP)₂ deposits on other substrates are formed of bigger spherical aggregated particles, of dimensions ranging from 200 to 300 nm in diameter on carbon cloth, expanding to 1 µm diameter on stainless-steel sheet, and reaching more than 2-3 µm diameter on Pt sheet. These discrepancy in film morphology and particles diameter can be attributed to the roughness, wettability and electrocatalytic effect of each current collector, which modulate the nuclei growth and kinetics, thus dictating the texture of the Ni₃(HITP)₂ films.[65]
<figure><img src="image_10.png" /><figcaption>**Figure 4.** Optical (left) and SEM (middle and right) images of the Ni₃(HITP)₂ film on various substrates electrodeposited from MeOH-DMSO electrolytic bath by pulsed potentiostatic method: (A) on Pt sheet, (B) on stainless steel sheet, (C) on vanadium nitride coated on Si/Si₃N₄ substrate, and (D) on carbon cloth.</figcaption></figure>

The optimized deposition method was also applied on 3D nanostructured substrates, with the aim to shape Pt@Ni₃(HITP)₂ core-shell nanowire (Figure 5A) and template Ni₃(HITP)₂ nanotube scaffolds (Figure 5B) that are expected to augment the target performances owing to the 3D nanoarchitectured scaffolds.[66–68] The potentiostatic pulsed deposition of Ni₃(HITP)₂ in MeOH-DMSO electrolytic bath on an interconnected Pt nanowire network substrate (Figure 5A-i.), resulted the formation of the core-shell nanostructures (Figures S8, S9). A uniform Ni₃(HITP)₂ shell-layer of 55 nm thickness was grown by applying a charge density of 650 mC.cm⁻². SEM unveiled the typical texture of Ni₃(HITP)₂ film covering the surface of each Pt nanowire (Figure 5A-ii), with the core-shell morphology confirmed by TEM (Figure 5A-iii). Similarly, the synthesis of Ni₃(HITP)₂ nanotubes was realized by pulsed potentiostatic
<figure><img src="image_9.png" /><figcaption>**Figure 4.** Optical (left) and SEM (middle and right) images of the Ni₃(HITP)₂ film on various substrates electrodeposited from MeOH-DMSO electrolytic bath by pulsed potentiostatic method: (A) on Pt sheet, (B) on stainless steel sheet, (C) on vanadium nitride coated on Si/Si₃N₄ substrate, and (D) on carbon cloth.</figcaption></figure>

The optimized deposition method was also applied on 3D nanostructured substrates, with the aim to shape Pt@Ni₃(HITP)₂ core-shell nanowire (Figure 5A) and template Ni₃(HITP)₂ nanotube scaffolds (Figure 5B) that are expected to augment the target performances owing to the 3D nanoarchitectured scaffolds.[66-68] The potentiostatic pulsed deposition of Ni₃(HITP)₂ in MeOH-DMSO electrolytic bath on an interconnected Pt nanowire network substrate (Figure 5A-i.), resulted the formation of the core-shell nanostructures (Figures S8, S9). A uniform Ni₃(HITP)₂ shell-layer of 55 nm thickness was grown by applying a charge density of 650 mC.cm⁻². SEM unveiled the typical texture of Ni₃(HITP)₂ film covering the surface of each Pt nanowire (Figure 5A-ii), with the core-shell morphology confirmed by TEM (Figure 5A-iii). Similarly, the synthesis of Ni₃(HITP)₂ nanotubes was realized by pulsed potentiostatic
deposition using an interconnected track-etched polycarbonate template membrane (pore diameter of 230 nm). The deposition was achieved by applying the total charge of ~ 2 C.cm⁻² leading to a Ni₃(HITP)₂ nanotube network, as revealed after the dissolution of the template (Figure 5B). The height of scaffold network was estimated at 15 µm, displaying good mechanical robustness (Figure S10). The nanotubes have a wall thickness of 70 nm with an outer diameter of 230 nm (as replication of the template). The diffusion of reactant species within the pores acts as the rate-determining step in Ni₃(HITP)₂ deposition, leading to the partial filling of the pores with HATP, particularly concentrated along the peripheral walls of the pores throughout the deposition, resulting in the hollow cylindrical (nanotube) morphology.[⁶⁹] Such configurations of core-shell nanowire and nanotube networks have the potential to enhance the accessibility of the Ni₃(HITP)₂ surface area, while shortening the diffusion path of ions as compared to the bulk film morphology. Furthermore, it can be expected that Pt@Ni₃(HITP)₂ nanowire network offers higher electrical conductivity and mechanical stability relative to the pure bulk Ni₃(HITP)₂ by the synergetic effect of combining Pt and Ni₃(HITP)₂ constituents in one single nanostructure.[⁷⁰]

<figure><img src="image_11.png" /><figcaption>B</figcaption></figure>

<figure><img src="image_12.png" /></figure>

**Figure 5.** (A-i.) Schematic illustration of the Pt@Ni₃(HITP)₂ core-shell nanowire network. (A-ii) SEM image of the Pt@Ni₃(HITP)₂ nanowire network and (A-iii.) TEM image showing the Pt core and Ni₃(HITP)₂ shell composing the nanowire network. (B-i.) Schematic illustration of Ni₃(HITP)₂ nanotube network. (B-ii.) Wide view and (B-iii.) high resolution SEM image of the Ni₃(HITP)₂ nanotube network. (B-iv.) TEM image highlighting a Ni₃(HITP)₂ nanotube.

Pushing the concept further, Ni₃(HITP)₂ was deposited on Pt interdigit current collector electrodes to assemble a micro-supercapacitor (Figure 6A). The resulting microdevice made on Si wafer is composed of two Pt-Ni₃(HITP)₂ electrodes in an interdigit configuration. The
deposition using an interconnected track-etched polycarbonate template membrane (pore diameter of 230 nm). The deposition was achieved by applying the total charge of ~ 2 C.cm⁻² leading to a Ni₃(HITP)₂ nanotube network, as revealed after the dissolution of the template (Figure 5B). The height of scaffold network was estimated at 15 µm, displaying good mechanical robustness (Figure S10). The nanotubes have a wall thickness of 70 nm with an outer diameter of 230 nm (as replication of the template). The diffusion of reactant species within the pores acts as the rate-determining step in Ni₃(HITP)₂ deposition, leading to the partial filling of the pores with HATP, particularly concentrated along the peripheral walls of the pores throughout the deposition, resulting in the hollow cylindrical (nanotube) morphology.[⁶⁹] Such configurations of core-shell nanowire and nanotube networks have the potential to enhance the accessibility of the Ni₃(HITP)₂ surface area, while shortening the diffusion path of ions as compared to the bulk film morphology. Furthermore, it can be expected that Pt@Ni₃(HITP)₂ nanowire network offers higher electrical conductivity and mechanical stability relative to the pure bulk Ni₃(HITP)₂ by the synergetic effect of combining Pt and Ni₃(HITP)₂ constituents in one single nanostructure.[⁷⁰]

<figure><img src="image_10.png" /><figcaption>**Figure 5.** (A-i.) Schematic illustration of the Pt@Ni₃(HITP)₂ core-shell nanowire network. (A-ii) SEM image of the Pt@Ni₃(HITP)₂ nanowire network and (A-iii.) TEM image showing the Pt core and Ni₃(HITP)₂ shell composing the nanowire network. (B-i.) Schematic illustration of Ni₃(HITP)₂ nanotube network. (B-ii.) Wide view and (B-iii.) high resolution SEM image of the Ni₃(HITP)₂ nanotube network. (B-iv.) TEM image highlighting a Ni₃(HITP)₂ nanotube.</figcaption></figure>

Pushing the concept further, Ni₃(HITP)₂ was deposited on Pt interdigit current collector electrodes to assemble a micro-supercapacitor (Figure 6A). The resulting microdevice made on Si wafer is composed of two Pt-Ni₃(HITP)₂ electrodes in an interdigit configuration. The
$Ni_3(HITP)_2$ does not display a symmetric CV profile in the working potential window. Given the capacitance attained in the forward and reverse scans of the $Ni_3(HITP)_2$ is different, charge balance between the two electrodes was attained by tuning the thickness of the MOF film. By applying different electrodeposition charge on individual interdigit electrodes (Figure 6B), the symmetric $Pt-Ni_3(HITP)_2 / Pt-Ni_3(HITP)_2$ microdevice is fabricated and the electrochemical performance are evaluated. To this end, pulsed potentiostatic deposition in MeOH-DMSO electrolytic bath was conducted, with an electrodeposition charge of 100 µC and of 400 µC applied on each Pt current collector (Figure S11). CV of the $Ni_3(HITP)_2$ micro-supercapacitor, measured in the voltage window of 0-1.0 V at 5 V.s⁻¹, displayed a combination of rectangular shape voltammogram with a redox peaks around ~ 0.5 V. This translates into higher current delivery (normalized to the footprint surface) as compared to the bare uncoated Pt / Pt MSC (Figure S12). Electrochemical impedance spectroscopy (EIS) analysis of bare and $Ni_3(HITP)_2$ coated electrodes displayed an increased sloppy nature of the Nyquist plot at lower frequencies, corroborating the capacitive nature of coated electrodes (Figure S13-A.). However, the high solution resistance (inset of Figure S13-A.) indicates the increased interfacial resistance of $Ni_3(HITP)_2$. Further, the frequency plot (Figure S13-B.) attests the preservation of capacitive behaviour up to a characteristic frequency of 1160.7 Hz. It also pinpoints a remarkable relaxation time constant, $v_0$, of 0.9 ms, which signifies a high percentage of the useful capacitance inherent to $Ni_3(HITP)_2$ through a fast charging/discharging process. Importantly, a reduced value of $v_0$ is indicative of faster ion transport within the electrode.

Detailed electrochemical performance analysis of $Ni_3(HITP)_2$ micro-supercapacitors was undertaken using cyclic voltammetry, at different scan rates in two different voltage ranges in 1.0 M KOH aqueous electrolyte. The rectangular-shaped voltammograms while cycling in the limited voltage window of 0 - 0.5 V indicates pure double-layer capacitive storage mechanism, with an average areal capacitance of 0.27 mF.cm⁻² (Figure S14). Conversely, when operated in a wider voltage window of 0 - 0.8 V, an additional reversible redox behaviour is noted coming from the redox activity of $Ni_3(HITP)_2$, with an increased average areal capacity of 0.48 mF.cm⁻² (Figure 6C). These reversible oxidation and reduction peaks, observed around ~0.6V and ~0.3V respectively, are attributed to the reversible redox process centered on the HATP ligand.[4] The large difference in potential between the oxidation and reduction peaks is certainly due to the ultra-high scan rates used for the CV measurement from 1 to 10 V.s⁻¹.
$Ni_3(HITP)_2$ does not display a symmetric CV profile in the working potential window. Given the capacitance attained in the forward and reverse scans of the $Ni_3(HITP)_2$ is different, charge balance between the two electrodes was attained by tuning the thickness of the MOF film. By applying different electrodeposition charge on individual interdigit electrodes (Figure 6B), the symmetric $Pt-Ni_3(HITP)_2 / Pt-Ni_3(HITP)_2$ microdevice is fabricated and the electrochemical performance are evaluated. To this end, pulsed potentiostatic deposition in MeOH-DMSO electrolytic bath was conducted, with an electrodeposition charge of 100 µC and of 400 µC applied on each Pt current collector (Figure S11). CV of the $Ni_3(HITP)_2$ micro-supercapacitor, measured in the voltage window of 0-1.0 V at 5 V.s⁻¹, displayed a combination of rectangular shape voltammogram with a redox peaks around ~ 0.5 V. This translates into higher current delivery (normalized to the footprint surface) as compared to the bare uncoated Pt / Pt MSC (Figure S12). Electrochemical impedance spectroscopy (EIS) analysis of bare and $Ni_3(HITP)_2$ coated electrodes displayed an increased sloppy nature of the Nyquist plot at lower frequencies, corroborating the capacitive nature of coated electrodes (Figure S13-A.). However, the high solution resistance (inset of Figure S13-A.) indicates the increased interfacial resistance of $Ni_3(HITP)_2$. Further, the frequency plot (Figure S13-B.) attests the preservation of capacitive behaviour up to a characteristic frequency of 1160.7 Hz. It also pinpoints a remarkable relaxation time constant, $v_0$, of 0.9 ms, which signifies a high percentage of the useful capacitance inherent to $Ni_3(HITP)_2$ through a fast charging/discharging process. Importantly, a reduced value of $v_0$ is indicative of faster ion transport within the electrode.

Detailed electrochemical performance analysis of $Ni_3(HITP)_2$ micro-supercapacitors was undertaken using cyclic voltammetry, at different scan rates in two different voltage ranges in 1.0 M KOH aqueous electrolyte. The rectangular-shaped voltammograms while cycling in the limited voltage window of 0 - 0.5 V indicates pure double-layer capacitive storage mechanism, with an average areal capacitance of 0.27 mF.cm⁻² (Figure S14). Conversely, when operated in a wider voltage window of 0 - 0.8 V, an additional reversible redox behaviour is noted coming from the redox activity of $Ni_3(HITP)_2$, with an increased average areal capacity of 0.48 mF.cm⁻² (Figure 6C). These reversible oxidation and reduction peaks, observed around ~0.6V and ~0.3V respectively, are attributed to the reversible redox process centered on the HATP ligand.[4] The large difference in potential between the oxidation and reduction peaks is certainly due to the ultra-high scan rates used for the CV measurement from 1 to 10 V.s⁻¹.
<figure><img src="image_13.png" /><figcaption>**Figure 6.** (A) Optical photograph of the interdigit electrodes, and (B) SEM image of Ni₃(HITP)₂ coated electrodes. (C) Cyclic voltammograms of Ni₃(HITP)₂ micro-supercapacitor in 1M KOH aqueous electrolyte at different scan rates. (D) Analysis of the cyclic voltammogram acquired at a scan rate of 5V·s⁻¹, differentiating the non-diffusive current (shaded region) from the total current (blue line). (E) Histogram showing the percentage of non-diffusive nature contribution to the stored charge at different scan rates. (F) Cyclic voltammograms at scan rate of 5V·s⁻¹ showing the stability of the device over 1.000 cycles.</figcaption></figure>

To confirm the rate capability of the fabricated micro-supercapacitors, we studied kinetics limitation at the electrode level. From the kinetics analysis the Ni₃(HITP)₂ electrodes show an anodic **b**-value of 0.63 and a cathodic **b**-value of 0.87, testifying the heightened ion-diffusion limitation during anodic process relative to cathodic process (detailed analysis is provided as note to Figure S15 in SI). The non-diffusion contribution of Ni₃(HITP)₂ was quantified employing the power law (Figure S15).[71] The evaluation of the non-diffusion-limited coefficient **a**₁ and diffusion-limited coefficient **a**₂ (by mathematical considerations described in the caption of Figure S16) allows quantifying both diffusion and non-diffusion limited contributions. For instance, the cyclic voltammogram exhibit a non-diffusion behaviour of 65% at a scan rate of 5 V·s⁻¹ (shaded region, Figure 6D). This proportion amplifies at higher scan rates, reaching up to 75% at 10V·s⁻¹ (Figure 6E) promoting fast redox process.

Finally, the stability of the Ni₃(HITP)₂ micro-supercapacitor was confirmed by performing CV experiments over 1.000 cycles at a scan rate of 5 V·s⁻¹, in both tested voltage windows of 0 – 0.5V and 0 – 0.8V (Figure 6F), with no visible change in the capacitive regimes (0 – 0.5V) observed, which indicates high stability of the device. Minor changes are noted the wide voltage
A

<figure><img src="image_11.png" /></figure>

C

<figure><img src="image_12.png" /></figure>

E

<figure><img src="image_13.png" /></figure>

B

<figure><img src="image_14.png" /></figure>

D

<figure><img src="image_15.png" /></figure>

F

<figure><img src="image_16.png" /></figure>

**Figure 6.** (A) Optical photograph of the interdigit electrodes, and (B) SEM image of Ni₃(HITP)₂ coated electrodes. (C) Cyclic voltammograms of Ni₃(HITP)₂ micro-supercapacitor in 1M KOH aqueous electrolyte at different scan rates. (D) Analysis of the cyclic voltammogram acquired at a scan rate of 5V·s⁻¹, differentiating the non-diffusive current (shaded region) from the total current (blue line). (E) Histogram showing the percentage of non-diffusive nature contribution to the stored charge at different scan rates. (F) Cyclic voltammograms at scan rate of 5V·s⁻¹ showing the stability of the device over 1.000 cycles.

To confirm the rate capability of the fabricated micro-supercapacitors, we studied kinetics limitation at the electrode level. From the kinetics analysis the Ni₃(HITP)₂ electrodes show an anodic **b**-value of 0.63 and a cathodic **b**-value of 0.87, testifying the heightened ion-diffusion limitation during anodic process relative to cathodic process (detailed analysis is provided as note to Figure S15 in SI). The non-diffusion contribution of Ni₃(HITP)₂ was quantified employing the power law (Figure S15).[71] The evaluation of the non-diffusion-limited coefficient **a**₁ and diffusion-limited coefficient **a**₂ (by mathematical considerations described in the caption of Figure S16) allows quantifying both diffusion and non-diffusion limited contributions. For instance, the cyclic voltammogram exhibit a non-diffusion behaviour of 65% at a scan rate of 5 V·s⁻¹ (shaded region, Figure 6D). This proportion amplifies at higher scan rates, reaching up to 75% at 10V·s⁻¹ (Figure 6E) promoting fast redox process.

Finally, the stability of the Ni₃(HITP)₂ micro-supercapacitor was confirmed by performing CV experiments over 1.000 cycles at a scan rate of 5 V·s⁻¹, in both tested voltage windows of 0 – 0.5V and 0 – 0.8V (Figure 6F), with no visible change in the capacitive regimes (0 – 0.5V) observed, which indicates high stability of the device. Minor changes are noted the wide voltage
window (0 – 0.8V), albeit without losing the reversibility, further confirming the robustness
and stability of the assembled Ni₃(HITP)₂ based micro-supercapacitors.

**4. Conclusion**

We demonstrated the non-sacrificial anodic deposition of homogeneous and crystalline Ni₃(HITP)₂ films on various current collectors for micro-supercapacitor applications. SEM analysis revealed the films morphologies constituted of aggregated Ni₃(HITP)₂ primary particles, collectively grown in homogeneous stable and thick films that can be integrated onto any desired conductive substrate. Applying pulsed deposition of Ni₃(HITP)₂ in MeOH-DMSO electrolytic bath proved to be the most suitable technique to prepare step-conformal crystalline films on various nanoarchitectured scaffolds. The optimized electrodeposition method was further successfully employed to fabricate nanoarchitectures, including Pt@Ni₃(HITP)₂ core-shell nanowires, nanotube networks, and uniformly coated fine-scale interdigit micro-supercapacitors. The microdevices exhibited good electrochemical performances and ultra-high rate capability. For future perspectives, the direct non-sacrificial anodic deposition approach of Ni₃(HITP)₂ could be extrapolated to accommodate conformal films of other MOFs with analogous functionalities such as hexaminobenzene structures. The method could be adapted to other conductive MOFs based on redox-active functionalized ligand, such as triphenylene (with functional O,O' ; N,N' ; S,S'), benzene (hexaoxy-, hexamino-, hexathiol-) and derivatives. Complementary, other centers could be used, by using transition metal (e.g. with Co, Ni, Fe, Cu ions) or lanthanide ions (e.g. La, Nd, Eu ions) that should be feasible vis the non-sacrifical route.[52,72] A compromise should be nevertheless found, particularly if both metal and ligand species are redox active (this being responsible for the formation of impure or multiphase materials). The parameters of electrodeposition are pivotal for each new MOF combination: the working potential, the composition of the electrolytic bath (nature and volume of solvents, metal:ligand ratio, nature and amount of additives such as base, the pH), the electrodeposition method, the substrate. Hence, the direct non-sacrificial anodic deposition method is considered to open doors towards the integration of conductive MOF films in advanced microelectronic applications.

**Supporting Information**

Supporting Information is available from the Wiley Online Library or from the author.
window (0 – 0.8V), albeit without losing the reversibility, further confirming the robustness
and stability of the assembled Ni₃(HITP)₂ based micro-supercapacitors.

**4. Conclusion**

We demonstrated the non-sacrificial anodic deposition of homogeneous and crystalline Ni₃(HITP)₂ films on various current collectors for micro-supercapacitor applications. SEM analysis revealed the films morphologies constituted of aggregated Ni₃(HITP)₂ primary particles, collectively grown in homogeneous stable and thick films that can be integrated onto any desired conductive substrate. Applying pulsed deposition of Ni₃(HITP)₂ in MeOH-DMSO electrolytic bath proved to be the most suitable technique to prepare step-conformal crystalline films on various nanoarchitectured scaffolds. The optimized electrodeposition method was further successfully employed to fabricate nanoarchitectures, including Pt@Ni₃(HITP)₂ core-shell nanowires, nanotube networks, and uniformly coated fine-scale interdigit micro-supercapacitors. The microdevices exhibited good electrochemical performances and ultra-high rate capability. For future perspectives, the direct non-sacrificial anodic deposition approach of Ni₃(HITP)₂ could be extrapolated to accommodate conformal films of other MOFs with analogous functionalities such as hexaminobenzene structures. The method could be adapted to other conductive MOFs based on redox-active functionalized ligand, such as triphenylene (with functional O,O' ; N,N' ; S,S'), benzene (hexaoxy-, hexamino-, hexathiol-) and derivatives. Complementary, other centers could be used, by using transition metal (e.g. with Co, Ni, Fe, Cu ions) or lanthanide ions (e.g. La, Nd, Eu ions) that should be feasible vis the non-sacrifical route.[52,72] A compromise should be nevertheless found, particularly if both metal and ligand species are redox active (this being responsible for the formation of impure or multiphase materials). The parameters of electrodeposition are pivotal for each new MOF combination: the working potential, the composition of the electrolytic bath (nature and volume of solvents, metal:ligand ratio, nature and amount of additives such as base, the pH), the electrodeposition method, the substrate. Hence, the direct non-sacrificial anodic deposition method is considered to open doors towards the integration of conductive MOF films in advanced microelectronic applications.

**Supporting Information**

Supporting Information is available from the Wiley Online Library or from the author.
## Acknowledgements

S.B, J.O, L.P and A.V. acknowledge the CF-ARC grant (18/23-093) MICROBAT for financial support. G.C. acknowledges the Belgian Fonds de la recherche scientifique (F.R.S.-FNRS) for FRIA fellowship. A.V. acknowledges funding from the European Research Council (ERC) grant-project 770870-MOOiRE. The authors acknowledge Dr. Fabien Drault for assisting D. M. with TEM analysis. The authors would like to thank the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01 and MEMPACAP ANR project). The French RENATECH network and the University of Lille are greatly acknowledged for supporting the Center of MicroNanoFabrication (CMNF) facility from IEMN. This work received funding from the CPER Hauts de France projects, IMITECH and MEL.

Dr. S. Behboudikhiavi and G. Chanteux equally contributed to this work.

Received: ((will be filled in by the editorial staff))

Revised: ((will be filled in by the editorial staff))

Published online: ((will be filled in by the editorial staff))

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## Acknowledgements

S.B, J.O, L.P and A.V. acknowledge the CF-ARC grant (18/23-093) MICROBAT for financial support. G.C. acknowledges the Belgian Fonds de la recherche scientifique (F.R.S.-FNRS) for FRIA fellowship. A.V. acknowledges funding from the European Research Council (ERC) grant-project 770870-MOOiRE. The authors acknowledge Dr. Fabien Drault for assisting D. M. with TEM analysis. The authors would like to thank the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01 and MEMPACAP ANR project). The French RENATECH network and the University of Lille are greatly acknowledged for supporting the Center of MicroNanoFabrication (CMNF) facility from IEMN. This work received funding from the CPER Hauts de France projects, IMITECH and MEL.

Dr. S. Behboudikhiavi and G. Chanteux equally contributed to this work.

Received: ((will be filled in by the editorial staff))

Revised: ((will be filled in by the editorial staff))

Published online: ((will be filled in by the editorial staff))

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**Title**: Direct Electrodeposition of Electrically Conducting Ni₃(HITP)₂ MOF Nanostructures for Micro-Supercapacitor Integration

**TOC Summary**: Direct anodic and non-sacrificial electrochemical deposition of an electrically conducting MOF Ni₃HITP₂, on a variety of metallic, semiconducting and carbon substrates, with fine control over nanostructured architectures is reported. Ni₃HITP₂ MOF is integrated within micro-supercapacitor interdigit device, using the method developed thereof, with enhanced capacitive storage and cycling stability.

<figure><img src="image_14.png" /></figure>
**Title**: Direct Electrodeposition of Electrically Conducting Ni₃(HITP)₂ MOF Nanostructures for Micro-Supercapacitor Integration

**TOC Summary**: Direct anodic and non-sacrificial electrochemical deposition of an electrically conducting MOF Ni₃HITP₂, on a variety of metallic, semiconducting and carbon substrates, with fine control over nanostructured architectures is reported. Ni₃HITP₂ MOF is integrated within micro-supercapacitor interdigit device, using the method developed thereof, with enhanced capacitive storage and cycling stability.

<figure><img src="image_17.png" /></figure>