bluuebunny/crossref_metadata_2025 huggingface dataset:
Core-Shell Structured Water Oxidation Anode for Minimum Platinum Group Metal Usage in Proton Exchange Membrane Water Electrolyzer
Authors: Jeong Hui-Yun , Oh Jinho , Yi Gyu Seong , Park Hyun S.
Published: September 2023

The development of enhanced electrocatalysts and optimization of electrode structures are of great importance for the practical and widespread deployment of proton exchange membrane water electrolyzers (PEMWEs). In particular, the scarcity and high price of Ir are considered to be bottlenecks inhibiting the large-scale commercialization of PEMWEs. Even compared with Pt, a rare-earth metal with a low production rate of 150~200 tons per year, Ir availability is extremely limited, as only a few tons per year are produced [1]. Therefore, It is envisioned that the Ir loading on the anode should be lowered (e.g., to 0.05 mg/cm2) to meet the annual demand for the PEMWE system installation on the scale of ≈5 GW by 2040 [2].

To reduce the usage of rare-earth metals in PEMWEs, a highly active water-oxidizing anode was fabricated by depositing a core–shell structured catalyst on a titanium porous transport layer (Ti PTL). Earth-abundant metal-based iron-nitride (Fe2N) nanostructure was deposited on a Ti PTL by sequential hydrothermal and nitridation reaction. The prepared Fe2N nanostructure was then passivated by thin, electrodeposited iridium-oxide films (EIROF). Fe2N@EIROF core-shell structured anodes exhibited substantially low ohmic and mass-transfer resistances, leading to a high current density of 4.50 A/cm2 (@1.9 Vcell). The unique Fe2N@EIROF core-shell structure enhanced PEMWE performance in terms of Ir mass activity by substituting inner Ir atoms with earth-abundant metal-based iron nitride. A high Ir mass activity of 103 A/mgIr (@1.9 Vcell) was achieved by reducing Ir loading amount to 0.064 mg/cm2 on the anode. The chemical instability of transition metal-based supports in a PEMWE operating condition was overcome by the passivation with Ir catalyst layers. As a result, the prepared core–shell-structured catalysts were stable under the PEMWE operating condition achieving high Ir mass activities.

[1] K. Nose, T.H. Okabe, Chapter 2.10 - Platinum Group Metals Production, in: S. Seetharaman (Ed.) Treatise on Process Metallurgy, Elsevier, Boston, 2014, pp. 1071-1097,

[2] C. Minke, M. Suermann, B. Bensmann, R. Hanke-Rauschenbach, Is iridium demand a potential bottleneck in the realization of large-scale PEM water electrolysis?, Int. J. Hydrogen Energy, 46 (2021) 23581-23590
(Digital Presentation) Electrospun Bimetallic Cu/Zn Selenide @ Carbon Nanofiber Electrocatalysts for Oxygen Evolution and Oxygen Reduction
Authors: Velpandian Muthuraja , Meduri Praveen
Published: September 2023

Electrochemical water splitting and fuel cells are intriguing ways to achieve a potentially sustainable and clean energy1. A greater focus on these energy technologies necessitates the design and development of highly active, cost-effective electrocatalysts that can substitute state of the art noble metal based materials2. In this context, metal selenide-based materials are important owing to their superior stability and electrical conductivity3. Their high specific surface area and abundant active sites on the surfaces make them strong candidates for use as electrocatalysts. Herein, heterostructured copper selenide and zinc selenide encased in carbon nanofibers (CZSe@C-450) synthesized using electrospinning and selenization techniques are used as bifunctional electrocatalysts. The novel architecture and tunable confinement of bimetallic selenides with the carbon matrix results in improved electrochemical performance in both oxygen evolution (OER) and oxygen reduction reactions (ORR)4. CZSe@C-450 exhibits a low overpotential of 260 mV at 10 mA cm−2 for oxygen evolution reaction and exhibits a half-wave potential (E1/2) of 0.88 V for oxygen reduction reaction. Further, the creation of a heterogeneous phase boundary between copper selenide and zinc selenide in the CZSe@C-450 enhances the built-in potential, local atomic disorder, and mismatch in the lattice that leads to lowering the surface energy. This gives rise to creation of catalytically active edge sites and phase boundaries, which contribute to the enhanced performance and good stability in both OER and ORR5,6.

References:

(1) Gielen, D.; Taibi, E.; Miranda, R. Hydrogen: A Renewable Energy Perspective. Abu Dhabi: International Renewable Energy Agency
2019.

(2) Han, L.; Dong, S.; Wang, E. Transition‐metal (Co, Ni, and Fe)‐based Electrocatalysts for the Water Oxidation Reaction. Advanced materials
2016, 28 (42), 9266–9291.

(3) Feng, W.; Pang, W.; Xu, Y.; Guo, A.; Gao, X.; Qiu, X.; Chen, W. Transition Metal Selenides for Electrocatalytic Hydrogen Evolution Reaction. ChemElectroChem
2020, 7 (1), 31–54. https://doi.org/10.1002/celc.201901623.

(4) Velpandian, M.; Ummethala, G.; Malladi, S. K.; Meduri, P. Heterogeneous Interface Induced Electrocatalytic Efficiency Boosting of Bimetallic Cu/Zn Selenides for Stable Water Oxidation and Oxygen Reduction Reactions. Catalysis Science & Technology
2022.

(5) Gbadamasi, S.; Mohiuddin, M.; Krishnamurthi, V.; Verma, R.; Khan, M. W.; Pathak, S.; Kalantar-Zadeh, K.; Mahmood, N. Interface Chemistry of Two-Dimensional Heterostructures – Fundamentals to Applications. Chem. Soc. Rev.
2021, 50 (7), 4684–4729. https://doi.org/10.1039/D0CS01070G.

(6) Zhao, R.; Li, Q.; Jiang, X.; Huang, S.; Fu, G.; Lee, J.-M. Interface Engineering in Transition Metal-Based Heterostructures for Oxygen Electrocatalysis. Mater. Chem. Front.
2021, 5 (3), 1033–1059. https://doi.org/10.1039/D0QM00729C.
(Invited) Insights into Electrochemistry and Associated Transport Processes in Scalable Batteries
Authors: Takeuchi Esther S. , Takeuchi Kenneth J. , Marschilok Amy C.
Published: September 2023

Batteries are complex systems based on heterogeneous structures that operate far from equilibrium. Pursuit of fundamental understanding over multiple length scales remains critically important to effectively design materials and electrode architectures to ensure that the functional properties of the energy storage systems meet the needs of future applications. As scalable systems are pursued, the fundamental properties determining the behavior of the batteries must be considered. Thermodynamic factors ultimately determine stability, however, kinetic factors involving ion and electron transport as well as electron transfer determine the practical utilization of the battery. Mechanisms of charge storage in aqueous electrolyte batteries and the role and control of dynamic interphases will be discussed. Insights into the relevant mechanisms and their associated transport processes as gained through the use of operando and in-situ methods will be featured.
MnOx Co-Catalysts Improved the Photoelectrochemical Properties of Fe2O3
Authors: Rohilla Jyoti , Lai Ting-Hsuan , Wang Chien-Yi , Tsao Chun-Wen , Gahlawat Soniya , Ingole Pravin p , Hsu Yung-Jung
Published: September 2023

The associated use of limited fossil fuels has also aroused an urgent need to seek for alternative, renewable energy sources. In this regard, hydrogen is the potential and green alternative to replace fossil fuels. Photo-electrochemical (PEC) water splitting towards the production of hydrogen is one of research hotspots, which has received significant attention due to its easy setup and great flexibility for further integrating with energy conversion and storage systems. Hematite (Fe2O3) has been widely utilized in photoelectrochemical (PEC) cells due to its suitable band gap and high electrochemical stability. However, its efficiency is limited by poor charge dynamics and slow reaction kinetics. Surface modification with an amorphous MnOx co-catalyst has been adopted to improve the PEC efficiency of Fe2O3. In this work, the mechanistic origin of introducing amorphous nano-fibrous MnOx as co-catalysts on the PEC performance of Fe2O3 photoanodes has been explored. Introduction of MnOx over Fe2O3 with an optimized thickness results in enhanced efficiency towards PEC water splitting, showing four-fold enhanced photocurrent over bare Fe2O3. The improved PEC performance of Fe2O3/MnOx can be assigned to the synergistic effect between Fe2O3 and MnOx, which led to improved charge dynamics at interface, anodic shift of valence band and increased electrochemical active sites.
Quantification of the Stability of ALD-Grown TiO2 Protective Coatings on Photoanodes for Solar Water Splitting
Authors: Kollmann Jiri , Kriegel Herman , Raudsepp Ragle , Pourmahdavi Maryam , Klassen Thomas , Schieda Mauricio
Published: September 2023

Semiconducting photoabsorbers used in photoelectrochemical applications often exhibit low stability under operating conditions. One strategy implemented in recent years to prevent corrosion of photoelectrodes is the application of thin films of titanium dioxide (TiO2), coated by atomic layer deposition (ALD). However, the stability of these coatings under photoelectrochemical conditions is also limited. We are using spectroscopic ellipsometry (SE) and in-situ atomic force microscope (AFM) characterization[1, 2] in order to quantify the influence of the coating process parameters and of post-deposition treatments on the degradation of these protective layers. Here we show our recent investigations under anodic operation in acidic environment. For fully amorphous TiO2 layers, a significant contributor to the corrosion is a purely chemical process, with an activation energy of 57 kJ/mol. Furthermore, the degradation rate doubles upon illumination under simulated sunlight. With increasing pH, the stability increases significantly. Partially crystalline protective coatings exhibit improved stability under operating conditions in sulfuric acid.

References:

[1] Kriegel H. et al. J. Mater. Chem. A, 2020, 8, 18173.

[2] Raudsepp R. et al. (in preparation).

Figure 1
Electrochemical Impedance Spectroscopy of Amorphous TiO2 Protected Photocathodes Under Hydrogen Evolution Conditions
Authors: Service Erin , Moehl Thomas , Adams Pardis , Tilley S. David
Published: September 2023

Despite widespread use of electrochemical impedance spectroscopy (EIS) to study multi-layer photoelectrochemical (PEC) cells, the appropriate equivalent circuits describing these devices under hydrogen evolution conditions are not commonly investigated.1 This creates ambiguity with respect to the pathways of charge recombination and ionic movement within layers of the device during operation, therefore limiting rational development of future PEC devices. In this study, amorphous TiO2 (a-TiO2) protected silicon photocathodes have been investigated using EIS to show that these devices behave according to the Maxwell circuit during hydrogen evolution, which occurs when the semiconductor is in depletion. Therefore, there are two simultaneous processes occurring in parallel and on different timescales. While the high frequency component is the result of the depletion region in the semiconductor, the low frequency component of this circuit is found to originate from the a-TiO2 itself, implying a capacitive charging process of this protective overlayer during PEC cell operation. Studies to isolate the physical mechanism of capacitive charging in the a-TiO2 from a range of possibilities such as proton intercalation and vacancy migration have been carried out. This result is important for the development of future PEC devices using emerging semiconductors which heavily rely on the a-TiO2 overlayer in acidic electrolytes, such as Cu2O and Sb2Se3, where this low frequency process has previously been observed.1 Using the Maxwell circuit for a-TiO2 protected photocathodes under hydrogen evolution conditions, one can independently determine properties of the semiconductor, such as the depletion capacitance and doping density, and the protective overlayer in these PEC devices under hydrogen evolution conditions. With this baseline, EIS can continue to aid the development of PEC cells as additional overlayers are developed and tested for further performance improvements.

Yang, W. et al. Operando Analysis of Semiconductor Junctions in Multi-Layered Photocathodes for Solar Water Splitting by Impedance Spectroscopy. Adv. Energy Mater.
11, 2003569 (2021).

Figure 1
(Invited) New Approaches to Photoelectrochemical Cascade Reactions and Protection of Photoelectrodes
Authors: Greenaway Ann L
Published: September 2023

A half-century of research has positioned direct photoelectrochemical (PEC) fuel generation as a promising technology that still requires substantial development. Work on the hydrogen evolution reaction (HER) has provided a strong basis for realizing the generation of more complex fuels through the carbon dioxide reduction reaction (CO2RR), but multiple challenges remain. The CO2RR requires larger driving forces and integration of multiple catalysts in order to selectively generate multi-carbonproducts, while still presenting many unsolved issues from HER, such stabilizing photoelectrodes under operation. In this talk I will discuss advances in the integration of multiple catalytic microenvironments in a single photoelectrochemical device, and progress toward the stabilization of photoelectrodes for fuel generation.

First, I will highlight the adaptation of three-terminal tandem (3TT) photovoltaic technology to photoelectrochemical applications. In our 3TT devices, a two-junction III-V solar cell device has an additional contact, enabling two unique catalyst sites operating at different voltages under the same illumination. Idealized circuit modeling shows the promise of these 3TT devices compared to traditional two-terminal, two-junction devices, particularly with respect to spectral tolerance. We have adapted the structure of 3TT photovoltaics to function as PEC devices and developed multiple catalysts for integration into the two solution contact sites. We demonstrate progress toward light-driven cascade catalysis for multi-carbon CO2RR products.

Second, I will highlight our approaches to protective schemes for photoelectrodes: one which is independent of semiconductor chemistry, and one which is driven by that chemistry. In the first approach, transparent conductive encapsulants (TCEs) are demonstrated as photoabsorber-agnostic protective layers. Unlike many protection schemes, these TCEs can be applied to semiconductors post-processing and without substantial modification, providing facile and robust protection. We have characterized the electrochemical performance of TCEs and demonstrate their integration with multiple semiconductors for the reduction of methyl viologen as a proxy for PEC fuel formation. In the second approach, we use the knowledge generated over fifty years of photoelectrode research to develop a new material, ZnTiN2, which can be directly integrated with established semiconductors and which will degrade under PEC conditions. We leverage this degradation to create protective layers which may be self-healing, and demonstrate rapid refinement of ZnTiN2 optoelectronic properties enabling integration with other semiconductors in tandem configurations.
(Invited) Sustainable Nitrate Production by Photocatalytic Oxidation of Air
Authors: Zaim Abdelkarim , Pashkova Aneta , Burek Bastien O. , Bloh Jonathan Z.
Published: September 2023

Nitrates are essential compounds for the chemical industry and in particular fertilizer production and are therefore critical for our global food production. They are nowadays almost exclusively produced in centralized plants by burning ammonia, which presents a major energetic detour in which the majority of ammonia’s high energy content is lost as heat. It would be much more efficient to synthesize nitrates directly from the elements (i.e., air) instead.

It has been shown already that air can be oxidized using heterogenous photocatalysis in aqueous suspensions to yield nitrate. However, the low nitrogen solubility and the fact that nitrate will also be available as electron scavenger (back-reaction) limit the overall efficiency and performance. We have recently demonstrated that this reaction is also possible in the gas phase.[1] Air can be directly oxidized over illuminated TiO2 surfaces to nitrogen oxides, predominantly NO2, which can then subsequently be adsorbed into water to form nitric acid.[1] This approach circumvents the limitations of the aqueous phase as nitrogen and water content can be more freely controlled and nitrates are only formed on the subsequent step, suppressing the back-reaction.

Overall, this presents and interesting new synthesis approach to nitrates in a decentralized manner, which could then be the basis for sustainable (solar) fertilizers which are produced directly in the areas in which they are needed.[2] This circumvents the energetic retour via ammonia and also saves on storage and transportation costs and emissions.

In this talk we will present results of our first studies on this reaction, in particular which reaction parameters (such as humidity and light intensity) are critical for the reaction and what influence they have. This reveals first insights into possible reaction mechanisms which will then be discussed. Based on our screening experiments, we will also show which catalyst materials and potential co-catalysts are suited and discuss why that may be the case, further elaborating about the reaction mechanism and potential active sites. This information is then used to predict ideal catalyst materials in a knowledge-based catalyst design approach.

References:

[1] Pashkova, A.; Burek, B. O.; Bloh, J. Z. Sustainable Nitrate Production out of Thin Air: The Photocatalytic Oxidation of Molecular Nitrogen. Catal. Sci. Technol.
2022, 12 (9), 2755–2760, http://dx.doi.org/10.1039/D2CY00350C

[2] Comer, B. M.; Fuentes, P.; Dimkpa, C. O.; Liu, Y. H.; Fernandez, C. A.; Arora, P.; Realff, M.; Singh, U.; Hatzell, M. C.; Medford, A. J. Prospects and Challenges for Solar Fertilizers. Joule
2019, 3 (7), 1578–1605, http://dx.doi.org/10.1016/j.joule.2019.05.001
Improving the Nitrogen Reduction Reaction Activity of Ti2n Nitride Mxene through pH and Electrolyte Selection
Authors: Johnson Denis , Djire Abdoulaye
Published: September 2023

Electrochemical nitrogen reduction reaction (NRR) is used to convert atmospheric nitrogen (N2) to ammonia (NH3) at ambient temperature and pressure. In general, acidic electrolytes are used to provide protons (H+) for the reduction process. However, this leads to a low NH3 selectivity because of H2 by-product formation via the hydrogen evolution reaction (HER). Recently, we showed that a Ti2N MXene is active and selective for NRR. We demonstrated that this catalyst works through a Mars-van Krevelen (MvK) mechanism rather than the conventional associative/dissociative mechanisms. However, the effect of pH and electrolyte on its catalytic activity and selectivity was not well understood. Here, we investigate these effects by performing experiments in varying electrolytic conditions and develop relations between pH, electrolyte choice, and performance. The Ti2N nitride MXene was synthesized via an oxygen-assisted molten salt fluoride etching technique and characterized through XRD and Raman and FTIR spectroscopies. Our findings showed that changing pH does not affect the NRR onset potential. We found that as pH increases, selectivity towards NH3 also increases presumably due to a lack of free H+ available to participate in HER. We also found that smaller cations with smaller solvation shells suppress HER activity, while smaller anions prevent catalyst poisoning during the NRR process, as evidenced by cyclic voltammetry before and after experimental conditions. We confirm production rates and the method of NH3 formation via NMR analytical techniques, including isotopic exchange. We plan to expand these findings to other materials and systems, and use the knowledge obtained from these studies to design optimal electrolytic conditions to produce NH3 through NRR.
(Invited) Nitroxyl-Derivatives As Cocatalyst for Lignin Decomposition by Dye-Sensitized Photoelectrochemical Cell
Authors: Kang Hyeong Cheol , Leem Gyu , Lee Jae-Joon
Published: September 2023

For stable and chemoselective decomposition of lignin model compound by DSPEC, metal based sensitizer was replaced by organic dye, 5-[4-(diphenylamino)phenyl]thiophene-2-cyanoacrylic acid (L1). For effective regeneration of dyes and oxidation of lignin model compounds(LMCs), bicyclic nitroxyl derivates, such as 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and 9-azabicyclo[3,3,1]nonan-3-one-9-oxyl (Keto-ABNO) were used. Keto-ABNO exhibited higher photo-electrocatalytic activity than TEMPO for the oxidation and decomposition of LMC. The superior reactivity with high selectivity of L1 sensitizer with Keto-ABNO mediator is attributed to the effective Caryl-Cα bond cleavage with 100% conversion yield for 24hrs at room temperature while it was 86% with TEMPO. The D–π–A type organic dye with a bicyclic nitroxyl radical mediator provides a possible strategic pathway for heterogeneous photocatalytic C–C bond cleavage at ambient condition.
(Invited) Z-Scheme Water Splitting Using Dye-Sensitized Metal Oxide Nanosheets
Authors: Maeda Kazuhiko
Published: September 2023

Solar water splitting by a heterogeneous photocatalyst, producing H2 and O2, is a potential solution for realizing large-scale H2 production. While dye-sensitized metal oxides are good candidates as H2 evolution photocatalysts for solar-driven Z-scheme water splitting, their solar-to-hydrogen (STH) energy conversion efficiencies remains low because of uncontrolled charge recombination reactions. Here it is shown that modification of Ru dye-sensitized, Pt- intercalated HCa2Nb3O10 nanosheets (Ru/Pt/HCa2Nb3O10) with both amorphous Al2O3 and poly(styrenesulfonate) (PSS) improves the STH efficiency of Z-scheme overall water splitting by a factor of ~100, when the nanosheets are used in combination with a WO3-based O2 evolution photocatalyst and an I3
–/I– redox mediator, relative to an analogous system that uses unmodified Ru/Pt/HCa2Nb3O10. The Al2O3 and PSS modifiers, which have previously been shown to suppress back electron transfer reactions in a dye-sensitized H2 evolution photocatalyst, enabled operation of the Z-scheme system even at low intensity of simulated sunlight without a decrease in the STH values. By using the optimized photocatalyst, PSS/Ru/Al2O3/Pt/HCa2Nb3O10, a maximum STH of 0.12% and an apparent quantum yield of 4.1% at 420 nm were obtained, by far the highest among dye-sensitized water splitting systems and also comparable to conventional semiconductor-based suspended particulate photocatalyst systems.
Coupled Lead Halide Perovskite Photoelectrode for Unbiased Photoelectrochemical Water Splitting
Authors: Rhee Ryan , Park Jong Hyeok
Published: September 2023

In search for new technology to preserve global warming caused by fossil fuel, solar energy driven devices have been high in demand. For instance, photovoltaics (PV) are a promising technology that can produce high power conversion efficiency (PCE). In addition, photoelectrochemical (PEC) water splitting, a promising artificial photosynthesis method, is a potential alternative technique to generate renewable fuel. PEC devices can generate renewable energy sources such as hydrogen, which can alleviate CO2 emission from fossil fuels. However, most readily employed PEC devices require external bias to function as a hydrogen producer. Thus, utilizing PV active layer as a photo absorber, PEC system is a suitable approach to the breakthrough of efficient hydrogen production.

In the past decade of PV technology advances, organic-inorganic lead halide perovskite (LHP) can be arguably the most progressive research because of its tunable bandgap, fast charge separation, broad light absorption spectra, low cost, facile fabrication, and high efficiency. These advantageous properties led LHPs to be used as an active layer of water splitting devices. However, LHP-based PECs have flaws to be addressed to be viable material for PEC. LHP are known for their fragile nature from exposure to water. Hence, LHP-based PECs are commonly protected with metal foil encapsulation while covering the edges with epoxy resins. However, the metal foil provides poor contact with the LHP leading to poor charge transfer for water splitting. To solve this problem, we applied carbon conductive powder (CCP) as the interlayer to successfully facilitate charge transfer.

With the proposed device modeling, monolithic PEC device that is capable of generating hydrogen in presence of low external applied bias is fabricated. Nonetheless, single monolithic PEC devices still need external applied bias to function as water splitting device which seek for further research. Therefore, adding another photoelectrode will eliminate the necessity of external bias resulting in an only solar powered water splitting device. Herein, we report unassisted solar to hydrogen conversion by using inverted and planar type LHP solar cells as photocathode and photoanode, respectively. With the integration of catalyst, 3D Ni.NiFe and NiPCoP, LHP-based PEC with exceptional performance was attained. We demonstrated unbiased PEC water splitting using a coupled LHP-based photoelectrode under alkaline conditions. Each LHP-based photoelectrode exhibited a outstanding performance of 22.42 mA cm-2 at 1.23 VRHE and 21.96 mA cm-2 at 0 VRHE for the photoanode and photocathode, respectively. Thus, we achieved solar to hydrogen (STH) of 10.64% and unassisted photo-current density of 8.65 mA/cm2. In addition, unbiased catalytic reactivity over 20 h retaining about 60% of photo-current density was attained.
Metal-Oxygen Hybridization of Bi/Bife(oxy)Hydroxide for Sustainable Lattice Oxygen Mechanism at High Current Density
Authors: Jo Seunghwan , Park Woon Bae , Ahn Docheon , Sohn Kee-Sun , Shin Ki Hoon , Hong John , Sohn Jung Inn
Published: September 2023

Hydrogen energy production through the electricity-driven water electrolysis has been broadly studied to deal with growing energy demands and environment pollutions. Oxygen evolution reaction (OER) which is the half anodic reaction of water electrolysis determines overall water electrolysis due to OOH* coordination with high energy barrier. Recently, alternative reaction kinetics detouring sluggish OOH intermediate in OER pathway has been proposed as breakthrough for efficient water electrolysis. That is the strategy which directly conjugates activated lattice oxygen species to form O-O coupling instead of OOH intermediate. However, absence of facile method to realize lattice oxygen activation and structural instability during OER cycles remain as challenge, hindering practical applications of water electrolysis. In this work, metal-oxygen hybridization method has been demonstrated as not only a simple and facile strategy to activate lattice oxygen species but also sustain lattice oxygen mechanism (LOM) during OER cycles at a practical current density (> 1000 mA cm-2). Using redox potential difference between bismuth (Bi) and iron (Fe) as driving force, galvanic replacement and Kirkendall effect take place in binary metal system, resulting in heterostructure composed of amorphous BiFe(oxy)hydroxides and molecular bismuth (Bi) metal nanoparticles (BM/BiFeOxHy) with abundant oxygen non-bonding states. In 1 M KOH solution, the BM/BiFeOxHy electrocatalyst requires low overpotential of 232 and 359 mV at the current densities of 10 and 1,000 mA cm-2, respectively. Moreover, long-term catalytic stability is demonstrated up to 1,000 hours at a practically high current density of 1,000 mA cm-2 without significant degradation by virtue of the balanced hybridization of Bi/Fe-O. Electrochemical/physicochemical analysis and density functional theory (DFT) calculation reveal that the excellent OER performance and stability of BM/BiFeOxHy electrocatalyst are attributed to the optimized Fe/Bi-O hybridization and resulting heterostructure with increased oxygen non-bonding states.
Electrochemical Growth and Restructuring of Cu Surfaces for Steering the Selectivity of Electrocatalytic CO2 Reduction
Authors: DuChene Joseph S
Published: September 2023

The electrocatalytic reduction of CO2 into value-added chemicals is commonly performed with catalysts composed of Cu due to its unique ability to create carbon-carbon bonds. Numerous studies have shown that the surface facets of the Cu catalyst play an important role on the observed distributions of both C1 products (i.e. carbon monoxide vs. methane) and C2 products (i.e. ethanol vs. ethylene). Here, we discuss our efforts towards controlling the surface facets of Cu electrocatalysts via electrochemical treatments for steering the selectivity of CO2 reduction in aqueous media. Using both planar Cu films and Cu nanoparticles, we will show how the applied potential and chemical composition of the growth solution can be manipulated to tailor the surface facets of Cu electrocatalysts. Finally, we will present the results of electrocatalytic CO2 reduction with these Cu catalysts and highlight opportunities for using simple electrochemical techniques to manipulate and control the surface facets of electrocatalysts for the production of chemical fuels.
(Invited) Electrocatalytic Conversion of CO2 to Syngas with Controlled CO/H2 Ratios
Authors: Chen Jingguang G
Published: September 2023

One of the main research challenges for electrocatalysis that produces carbon-containing products from CO2 is avoiding the competing hydrogen evolution reaction. Instead of totally eliminating hydrogen, our approach makes use of the readily available protons in aqueous electrolyte to co-produce CO and H2, making synthesis gas (syngas) with a tunable CO:H2 ratio. The resulting syngas can then be used as feedstock for existing thermocatalytic processes, such as Fischer–Tropsch and methanol synthesis reactions [1]. We will present our results in identifying palladium hydride (PdH), formed under electrocatalytic reaction conditions, as an effective electrocatalyst that enables the syngas production [2]. We will also report our efforts in reducing the loading of Pd by alloying Pd with inexpensive secondary metals, supporting Pd on transition metal carbides and nitrides, and utilizing single atom Pd catalysts. For each type of the catalysts, we monitor the phase transition from Pd to PdH under reaction conditions with in-situ synchrotron-based X-ray absorption and X-ray diffraction techniques. We also identify descriptors for syngas production on PdH, bimetallic PdH, and supported PdH catalysts by performing DFT calculations of the effect of PdH formation on the binding strength of reaction intermediates. The research methodology established here should be useful not only for continued optimization of Pd-based syngas-producing electrocatalysts, but also for enhancing activity while reducing the loading of precious metals for other electrocatalytic applications. Furthermore, we will discuss our recent results in utilizing a tandem scheme of electrocatalytic-thermocatalytic processes to convert CO2 to C3 oxygenates [3].

[1] B.M. Tackett, E. Gomez and J.G. Chen, “Net reduction of CO2 via its thermocatalytic and electrocatalytic transformation reactions in standard and hybrid processes”, Nature Catalysis, 2 (2019) 381.

[2] B.M. Tackett, J.H. Lee and J.G. Chen, “Electrochemical Conversion of CO2 to Syngas with Palladium-Based Electrocatalysts”, Accounts of Chemical Research, 53 (2020) 1535.

[3] A.N. Biswas, Z. Xie, R. Xia, S. Overa, F. Jiao and J.G. Chen, “Tandem Electrocatalytic-Thermocatalytic Reaction Scheme for CO2 Conversion to C3 Oxygenates”, ACS Energy Letters, 7 (2022) 2904
(Allen J. Bard Award in Electrochemical Science) Toward Electrochemical Energy Conversion Via Metal-Organic Framework Materials
Authors: Hupp Joseph
Published: September 2023

Consistent with the many energy-centric interests and pioneering contributions by Prof. Bard, this presentation will touch on catalytic electrochemical and photochemical energy conversion as enabled by metal-organic framework (MOF) materials. The presentation will focus on a couple of case studies that illustrate how nominally insulating MOF films can be persuaded to transport charge, deliver photo-generated molecular excitons, and catalytically drive energy-relevant, multi-electron chemical transformations.
(Invited) Carbon Nitride Layers As Light-Harvesting Semiconductors for Photoelectrochemical Cells
Authors: Shalom Menny
Published: September 2023

Photoelectrochemical cells (PECs) have been developed as environmentally friendly systems that can directly utilize photogenerated electron-hole pairs for water splitting, fuel production, conversion of carbon dioxide, and pollutant degradation. Most reports on the photocatalytic or PEC hydrogen (H2) evolution via water splitting have focused on the H2 reduction half-reaction by generating on the photoanode oxygen or using sacrificial agents to consume the generated h+. Lately, much effort has been invested into synthesizing valuable chemicals on the photoanode while retaining the production of H2 on the cathode.

Over the past few years, polymeric carbon nitrides (CN) have attracted widespread attention due to their outstanding electronic properties, which have been exploited in various applications, including photo- and electro-catalysis, heterogeneous catalysis, CO2 reduction, water splitting, light-emitting diodes, and PV cells. CN comprises only carbon and nitrogen, and it can be synthesized by several routes. Its unique and tunable optical, chemical, and catalytic properties, alongside its low price and remarkably high stability to oxidation (up to 500 °C), make it a very attractive material for photoelectrochemical applications. However, few reports regarded CN utilization in PECs due to the difficulty in acquiring a homogenous CN layer on a conductive substrate and our lack of a basic understanding of the intrinsic layer properties of CN.

This talk will introduce new approaches to growing CN layers with altered properties on conductive substrates for photoelectrochemical applications. The growth mechanism and their chemical, photophysical, electronic, and charge transfer properties will be discussed. I will show the utilization of PEC with a CN-based photoanode as a stable and efficient platform for the oxidation of water or organic molecules to oxygen or added-value chemicals, respectively, with hydrogen co-production.
(Invited) In-Situ Time-Resolved Probe of Charge Carrier Dynamics at Planar Semiconductor Photoelectrode/Liquid Interface
Authors: Lian Tianquan
Published: September 2023

Photoelectrochemistry is a promising approach for converting solar energy to storable chemical energy in chemical fuels. The efficiency of photoelectrochemcial devices depends critically on efficient transfer of charge carrier across the electrode liquid interface and the efficiency and selectivity of the catalytic reaction on electrode surface. Although transient absorption spectroscopy is a powerful tool for probing interfacial dynamics in high surface area electrodes, it is often not applicable on planar electrodes because the observed signal is often dominated by carrier dynamics in the bulk. In this talk, we discuss our recent effort in developing in situ time-resolved linear and nonlinear spectroscopic tools that can be used to probe carrier dynamics and reactions at planar electrode/liquid interfaces, focusing on transient reflection spectroscopy and electric field induced second harmonic generation (EFISH) spectroscopy. Compared to transient absorption, transient reflection spectroscopy is more sensitive to surface carrier density that can be more directly correlated to catalysis. We showed that transient reflectance change can be used to follow charge carrier dynamics and their amplitude can be directly correlated to efficiency of initial interfacial charge separation on p-GaP single crystals protected by TiO2 ALD layer. Our finding suggests that IPCE is determined by the product of the efficiency of initial ultrafast (< hundreds of ps) charge separation across the GaP/TiO2 interface and the efficiency of water reduction reaction on the slower time scale. Key loss pathways that limit these efficiencies are discussed. In a second approach, we showed the EFISH signal in a n-doped single crystal TiO2 can be used to probe the accumulation of photogenerated carriers at surface states and these trapped carriers are responsible for the water oxidation reaction.
(Invited) Understanding the Effects of Charge Distribution on the Oxidation of Water
Authors: Wang Dunwei
Published: September 2023

Water oxidation is an important first step of photosynthesis. Presently, it remains a challenge to carry out this reaction efficiently using low-cost materials. Among the questions that remain to be answered are the influences by charge distribution at or on the catalyst surfaces where water oxidation takes place. Recent literature has shown that the reaction can be sensitive to the charge density or the charge potential or both. Generally, high charge density or high charge potential favors faster kinetic constants. However, the existing studies face challenges as most of them were carried out on different materials that feature different chemical catalytic properties, as well. As such, it is not yet possible to definitely conclude the observed differences in water oxidation kinetics is necessarily a function of charge properties but not the inherent chemical catalytic differences. The study we plan to present addresses this issue. We used a catalyst system that features a well-defined catalytic center but employed supports that feature varying charge redistribution properties. This system allowed us to systematically compare how charge redistribution affects the water oxidation reactions. It was observed that when charge redistribution indeed plays an important role in defining the reaction kinetics, but it is so only when the subsequent chemical steps are fast. For the first time, we found a different dependence of the reaction kinetics on temperatures. Under otherwise identical conditions, comparable reaction kinetics were measured on ITO support and CeO2 support at room temperature. When the temperature increased to 50ºC, the reaction rate on ITO support increased to twice that on CeO2 support. The results shed new light on the role played by charge redistribution in governing reactions such as water oxidation.
(Invited) Who Shifts Where, When, and Why? Experimental Insights into Cu(In,Ga)(S,Se)2 Solar Absorbers for Photoelectrochemical Water Splitting
Authors: Heske Clemens
Published: September 2023

The electronic surface level positions of different chalcopyrite [Cu(In,Ga)(S,Se)2] thin-film solar absorbers are presented and their suitability for photoelectrochemical (PEC) water splitting is discussed. For efficient PEC water splitting, electrode surfaces must exhibit suitable band edge energies (i.e., the conduction band minimum, CBM, and the valence band maximum, VBM) to enable hydrogen and oxygen evolution. The VBM and CBM at the sample surfaces were experimentally derived under vacuum conditions using direct and inverse photoemission (XPS, UPS, and IPES). By measuring the work function at the surface, the band edge energies can be correlated to the normal hydrogen electrode and compared with the reduction and oxidation potentials necessary to drive PEC water splitting. By studying several chalcopyrite variants differing in growth process, composition, stoichiometry, and surface treatment, strategies are derived to optimize chalcopyrite PEC devices with respect to the redox potentials for solar water splitting.
(Invited) Design and Analysis of Electrolyte∣Catalyst∣Semiconductor Interface for Enhanced Photoelectrochemical Reactions
Authors: Lee Hyun Joo , Lim Sung Yul
Published: September 2023

Photoelectrochemical cells (PECs) enable the molecular synthesis, utilizing light energy and storing the charges into chemical bonds. In this way, PECs provide a renewable route to produce chemical fuels for carbon neutrality. Although various studies have been intensively conducted to achieve commercially viable PEC performance and costs, there are still several challenges for wide commercialization due to the complex functionality and connectivity in electrolyte∣catalyst∣semiconductor interfaces. Especially, more cautions are necessary when non-Pt group materials (NPGM) are utilized as catalysts. Much higher loading of NPGM is required than the one of PGM to compensate the relatively lower electrocatalytic activity, resulting in other issues including parasitic loss of photons. Here, functional integration of catalysts onto the semiconductor surface and analysis of the electrolyte∣catalyst∣semiconductor interface will be presented. The chemical compositions and spatio control of catalysts lead to the improved photoelectrochemical performance toward water splitting, resulting from the optimization of light absorption and transport/transfer of photogenerated charge carriers in crystalline silicon and hematite (α-Fe2O3). Furthermore, the impact of this catalyst manipulation is analyzed through electrochemical impedance and Raman spectroscopy to study the photoelectrochemical reaction pathways.
(Invited) Dynamic Electrochemical Interface for Oxygen Evolution Reaction
Authors: Chung Dong Young
Published: September 2023

The performance of electrochemical energy conversion reaction is determined by the charge and mass transfer at electrochemical interface since the electrochemical reaction occurs at the electrochemical interface between the electrode and the electrolyte. However, the understanding of the electrochemical interface is often overlooked, and most studies focus on the electrode (or the electrolyte) itself as a separate approach, hindering its application to electrochemical energy devices. Here, I will discuss the dynamic behavior in electrochemical interface in water electrolysis. Unlike the conventional ‘frozen’ interface, the properties of the dynamic interface are determined by the continuous chemical and electrochemical interaction between electrolyte and electrode, and based on this, it opens the possibility of new system that can overcome existing thermodynamic limitation and can accomplish ‘dynamic stability’, new types of stability in electrochemical interface level.
(Invited) Hybrid Mixed-Metal-Oxide-Based Catalytic Systems for Efficient Electroreduction of Carbon Dioxide
Authors: Kulesza Pawel J. , Rutkowska Iwona A.
Published: September 2023

Of particular interest to the preparation of advanced catalytic materials is efficient utilization of nanosized materials with well-defined composition, structure and thickness that exhibit desirable electrocatalytic properties. There has been growing interest in the electrochemical conversion of carbon dioxide (a potent greenhouse gas and a contributor to global climate change) to useful carbon-based fuels or chemicals. Given the fact that the CO2 molecule is very stable, its electroreduction processes are characterized by large over-potentials. It is often postulated that, during electroreduction, the rate limiting step is the protonation of the adsorbed CO product to form the CHO adsorbate. In this respect, the proton availability and its mobility at the electrochemical interface has to be addressed. On the other hand, competition between such parallel processes as hydrogen evolution and carbon dioxide reduction has also to be considered.

We explore here the ability of polynuclear transition metal oxide based systems to function as cocatalysts and to stabilize and activate metal nanocenters. Here certain nanostructured metal oxides of zirconium, titanium, molybdenum or tungsten have been demonstrated to influence supported catalytic metal sites in ways other than simple dispersion over electrode area. Evidence is presented that the support can modify activity (presumably electronic nature) of catalytic metal nanoparticles (e.g. Cu, Ru), thus affecting their chemisorptive and catalytic properties during CO2-reduction. Metal oxide (WO3, MoO3, TiO2) nanostructures can generate highly reactive –OH groups at electrocatalytic interface.

Evidence is presented that the support can modify activity (presumably electronic nature) of catalytic metal nanoparticles (e.g. Cu, Pd), thus affecting their chemisorptive properties. Metal oxide (ZrO2, WO3) nanospecies can generate –OH groups at electrocatalytic interface. Our electrocatalytic results with copper nanostructures over-coated with ZrO2 or WO3 nanostructures imply the systems’ improved selectivity toward CO2-reduction relative to the competitive hydrogen evolution as well as the lower tendency of copper sites to undergo poisoning.
Visible-Light Photocatalysis Design Using Non-Faceted Semiconductor/Liquid Junctions
Authors: Su Haoqing , Zhang Wentao , Liu Bin , He Chengxing , Yanagi Rito , Hu Shu
Published: September 2023

Photocatalysis has been shown as a promising fuel generation method due to its potential for low cost and high scalability. Narrow-bandgap semiconductors are good candidates for photocatalytic fuel production because of their high light absorbance and quantum efficiency; however, the instability and the small driving force for charge separation inhibit their broad utilization for solar fuel generation. Because of these factors, researchers have been struggling with making a narrow-band-gap photocatalytic panel. To surmount these limitations, we proposed a surface design strategy to manipulate the electrons and holes separation process without any facets design and build-in junction. Our modeling study shows that charge separation can be controlled by surface coating and catalyst design. The doping level of the semiconductors and the geometry of catalysts are the most important factors for charge separation efficiency. Based on this principle, we developed conformal coatings with attached nanoscale catalysts enabling planar III-V semiconductors for overall water splitting. With the atomic layer deposition, the coating of high conductivity was grown on the semiconductors to protect them and tune their band edge position for the desired fuel generation reactions. With E-beam lithography, the cathodic and anodic catalysts were designed to optimize the charge separation processes. Using these techniques, we fabricated GaP/(Ti,M)Ox/Ir/Rh@CrOx and InGaP/GaN/IrOx/Rh@CrOx panels and successfully achieved hydrogen and oxygen coevolution.

Figure 1
Electrocatalytic Oxidative Dehydrogenation of Aldehydes over Cu-Based Bimetallic Catalysts for Bipolar H2 Production with Industrially-Relevant Rates
Authors: Li Wenzhen , Liu Hengzhou , Chen Yifu , Yu Jiaqi , Huang Wenyu
Published: September 2023

Electrocatalytic oxidative dehydrogenation (EOD) of aldehydes enables ultra-low voltage, bipolar H2 production with co-generation of carboxylic acid. Herein, we presented a simple galvanic replacement method to prepare CuM (M= Pt, Pd, Au, and Ag) bimetallic catalysts to improve EOD of furfural to reach industrially-relevant current density. The redox potential difference between Cu/Cu2+ and a noble metal M/My+ can incorporate noble metal on Cu surface and enlarge its surface area. Particularly, dispersing Pt into Cu (CuPt) exhibits a unique synergistic effect for furfural EOD via efficient C-H cleavage on Cu and favorable furfural binding on Pt. The CuPt anode-based flow electrolyzer achieved a record-high current density of 498 mA cm−2 for bipolar H2 production at a low cell voltage of 0.6 V and faradaic efficiency of >80% to H2. The bimetallic catalysts hold potential for future distributed manufacturing of green hydrogen and carbon chemicals with practical rates and low-carbon footprints.