bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue-Free Electrodes Enabled Joule Heating Device for Wearable Thermotherapy
Authors: Xu Shujia , Wu Wenzhuo
Published: July 2021

Wearable Joule heating devices have received tremendous attention from researchers due to their applications in personal thermal management systems, like thermal management cloth, and healthcare application, such as wearable thermotherapy. Permeability, stretchability, dynamic stability, and conductivity are essential factors for electrothermal heating devices. Wearable devices usually work under cyclic loading of low stain, so fatigue, mechanical failure induced by cyclic loading at low strain level, is a common disease for metal electrodes. Fatigue-free materials are of great importance to ensure robustness for long-term application. Stretchable electrodes, such as noble metal nano mesh, conductive fillers-based elastomer and metal nanowires have been used to fabricate wearable heater. Liquid metal (LM) has also attracted lots of attention due to its high conductivity and fluidity at room temperature. Such fluidity not only makes LM attractive materials for flexible devices, but also render LM fatigue-free attribute. Many manufacturing methods, such as direct ink writing, screen printing and spray coating have been applied to fabricate LM based electrodes for flexible devices. Recently, electrospun technique have also been applied to fabricate LM particles doped polymer fibers, but LM based conductive fiber electrodes have not yet been fabricated using electrospun process. Here, a LM particles embedded fibers network electrode is fabricated using electrospun method, followed by wrapping a polymer layer on the fiber surface. The LM particles embedded in the electrospun fibers form interconnected network, which exhibits excellent electrical conductivity, high mechanical stretchability, and good fatigue performance. Such network electrode could be directly used as a Joule heater, which is permeable, stretchable and fatigue-free. High conductivity of the electrodes ensures low driving voltage for this electrothermal heating devices. High stretchability of the electrode ensures good Joule heating performance at high strain level. In addition, the uniform fibers size could induce large-scale uniform heating. The LM fiber electrodes could be cut into various patterns to fit curvilinear surface of human skin. Also, the ultrathin and compliant nature of the LM fiber electrode enable seamless attachment with human skin, which could ensure high thermal transfer efficiency. The combination of good electrical and mechanical performances of the LM fiber-based Joule heater enable long-term wearable thermotherapy.
(Invited) Soft Wireless Optofluidic and Optoelectronic Implants for Advanced Chronic Neural Interfacing
Authors: Jeong Jae-Woong
Published: July 2021

Optogenetics and neuropharmacology holds immense promise for dissection of neural circuits and cellular signaling in freely behaving animals. However, the full potential of their in vivo applications is limited by the use of conventional tools such as cannulas for drug delivery and fiber optics for photostimulation. These traditional approaches greatly damage neural tissue near the implant, hinder integration with different modalities, and severely limit the animal’s natural behavior and movement, mainly due to their rigid construction, bulky design, and tethered operation, respectively. Furthermore, current methods lack spatiotemporal control of drug delivery, wireless control, and multi-functionality.

To address these fundamental limitations in in vivo neuroscience, we have developed soft wireless optofluidic and optoelectronic implants, which can provide wireless delivery of light and/or drugs in awake, moving animals. The devices consist of ultrathin and flexible probes, which integrate microscale inorganic light-emitting diodes and/or microfluidic channels, and wireless interface with an independent power supply. This design enables compact, lightweight and soft system, thus enabling seamless implantation and operation in the brain without causing disturbance of naturalistic behavior. With integration of smartphone control, replaceable drug cartridges for long-term drug delivery, and wireless energy harvesters for intervention-free charging, they can further facilitate chronic neural interfacing to uncover the basis for brain functions and neuropsychiatric diseases. We have successfully demonstrated chronic wireless capabilities of these devices in freely moving animals that can repeatedly deliver multiple wavelengths of light and drugs for long periods of time to manipulate animals’ behavior. The unique capabilities of the soft wireless implants forecasts their broad utility in chronic in vivo neuropharmacology and optogenetics for various neuroscience research and clinical applications.
Phase Transitions in Correlated Oxides Modulated through Electrochemical Gating
Authors: Smieszek Nicholas , Joshi Siddharth , Chakrapani Vidhya
Published: July 2021

Strongly correlated oxides have many unusual properties, such as high-temperature superconductivity, colossal magnetoresistance, spin polarization, and metal-insulator phase transitions (MIT) that can be induced by various types of external stimuli, such as temperature, strain, pressure, electron and chemical doping, and light. VO2 undergoes an electronic and structural phase transition at 67°C from a non-magnetic monoclinic (M1) phase to a paramagnetic rutile (R) phase. Modulation of the transition temperature through oxygen over-stoichiometry is difficult to achieve in VO2 through annealing due to nucleation of the V2O5 phase within the VO2 lattice. However, electrochemical doping at room temperature using suitable electrolyte allows for systematic modulation of oxygen stoichiometry in VO2 through the regulation of charge carrier injection. Using this method, the oxygen stoichiometry in VO2 was modulated from 1.86 to 2.44 and its effects on the band structure and MIT was studied through detailed electrical and photoemission studies. In oxygen over-stoichiometric VO2 the TIMT was shifted from 67°C to 118°C, as shown in Figure 1.

The results offer a different perspective on the temperature- and doping-induced IMT process. They suggest that charge fluctuation in the metallic phase of intrinsic VO2 results in the formation of e− and h+ pairs that lead to delocalized polaronic V3+ and V5+ cation states. The metal-to-insulator transition is linked to the cooperative effects of changes in the V–O bond length, localization of V3+ electrons at V5+ sites, which results in the formation of V4+–V4+ dimers, and removal of π* screening electrons. It is shown that the nature of phase transitions is linked to the lattice V3+/V5+ concentrations of stoichiometric VO2 and that electronic transitions are regulated by the interplay between charge fluctuation, charge redistribution, and structural transition.

Figure 1
Quantifying Performance Improvements in MIEC-Infiltrated SOFC Anodes Using a Density of Relaxation Times Analysis of EIS Spectra
Authors: Rix Jillian , Mo Boshan , Pal Uday , Gopalan Srikanth , Basu Soumendra
Published: July 2021

To improve the intermediate-temperature performance of solid oxide fuel cells (SOFCs) and expand their applications requires mitigating anode activation polarization while maintaining long-term stability during use. The infiltration of nanoscale electrocatalysts into SOFC anodes has been shown to increase the number of reaction sites, thereby decreasing activation polarization. This study explores the impacts of liquid-phase infiltration of Ni and gadolinium-doped ceria (GDC), a Mixed Ionic and Electronic Conductor (MIEC), into both Ni-YSZ and Ni-MIEC anodes, where the YSZ has been doped with titanium dioxide to facilitate electronic conduction. Distribution of relaxation times (DRT) analysis is performed on Electrochemical Impedance Spectroscopy (EIS) spectra to deconvolute the kinetics of various charge transfer processes.

Figure 1
Electrochemical Oxidative Coupling of Methane to Produce Higher Hydrocarbons Using Sr2Fe1.5Mo0.5O6-Δ Electrocatalysts
Authors: Ramaiyan Kannan , Denoyer Luke H , Benavidez Angelica , Garzon Fernando H
Published: July 2021

Efficient conversion of methane to value added products such as olefins and aromatics has been in pursuit for the past several decades. The demand has increased further due to the recent discoveries of shale gas reserves (1). Oxidative and non-oxidative coupling of methane (OCM and NOCM) has been actively researched although commercially viable conversion rates have not been achieved with any catalyst yet. Electrochemical OCM is gaining attention due to its ability to control the oxide ion flux that will help reduce the over-oxidation of methane while also helping to activate methane. Recently, (SFMO-075Fe) has been reported to activate methane with a C2 product selectivity of 82.2% (2). However, alkaline earth metal-based materials are known to suffer chemical instability in carbon rich environments at elevated operating temperatures. Hence, we evaluated the chemical stability of SFMO-075Fe and SFMO in carbon rich conditions at temperatures relevance for EC-OCM. SFMO-075 showed wonderful methane activation properties but suffered poor chemical stability as observed in thermogravimetric and powder XRD measurements. XPS and XRD measurements revealed that SrCO3 as the major product along with MoC when SFMO is exposed to methane at 900°C. We further found that methane could be selectively activated towards partial oxidation products such as ethylene at low overpotentials while higher applied biases results in complete oxidation of methane to carbon dioxide and water. We report in this presentation our findings with SFMO along with potential benefits of EC-OCM for methane activation.

References

Schwach, X. Pan, and X. Bao, “Direct Conversion of Methane to Value-Added Chemicals over Heterogeneous Catalysts: Challenges and Prospects,” Chem. Rev., 117, 8497, 2017.

Zhu, S. Hou, X. Hu, J. Lu, F. Chen, and K. Xie, “Electrochemical conversion of methane to ethylene in a solid oxide electrolyzer,” Nat. Commun., 10, 1173, 2019.
Performance Degradation in Proton-Conducting Ceramic Electrochemical Cells
Authors: Le Long , Herradon Carolina , Meisel Charlie , Huang Jake , Ricote Sandrine , O'Hayre Ryan , Sullivan Neal P.
Published: July 2021

Proton-conducting ceramics are a promising new class of electrochemical cells with a lower-temperature operational range in comparison to more-conventional solid-oxide or molten-carbonate counterparts. In the past, we have successfully demonstrated the scalability of this technology from the button-cell to the lab-scale stacks shown in the figure, along with strong performance and stability over thousands of hours under methane fuel at 550 ºC. This encouraging result was achieved through careful tuning of materials, fabrication procedures, and operating conditions. We have found that the degradation rates of protonic-ceramics stacks can be intense, especially at lower temperatures under fuel-cell operating mode. We have observed lower degradation rates under electrolysis operation, and at higher operating temperatures. These are both perhaps counterintuitive; lower-temperature operation is expected to improve the long-term stability, and degradation is typically more pronounced for more-common solid-oxide electrolyzers. In this presentation, we will review our studies on the root causes of performance degradation in protonic ceramics, and approaches to mitigate degradation.

Previous work on performance degradation in oxygen-ion conducting electroceramics provides clues into the sources of degradation in protonic ceramics. That said, a number of degradation mechanisms are avoided by the nature of the protonic-ceramic device. For example, our microstructural characterizations reveal no nickel coarsening or agglomeration in the fuel electrode, likely due to the lower-temperature operation near 550 ºC. Operating conditions are shown to have a large impact on degradation rates in our protonic-ceramics; such conditions provide important clues about degradation’s root causes. Electrochemical Impedance Spectroscopy reveals how the slow kinetics of the electrochemical processes are closely tied to the degradation behaviors observed in our experiments.

While we will continue to explore our root causes of degradation in proton-conducting electrochemical cells, we also report the impact of a gadolinium-doped ceria (GDC) interlayer on improving the durability of the cells, especially at low temperatures. This is perhaps a surprising, as GDC is a common O2--conducting material, and perhaps ill-matched to protonic ceramics. Regardless, the presence of the GDC layer at the air electrode - electrolyte interface has proven to be an effective strategy for minimizing protonic-ceramics degradation throughout our research, falling to 1.2% / 1000 hr for the methane-fueled stack at 600 ºC. While the root causes of this performance improvement remain unclear, we find the use of the GDC interlayer to impactful in reducing performance degradation in protonic ceramics.

Figure 1
Zeolitic-Imidazolate-Framework-(ZIF)-Derived Coni Carbon Nanotubes As Bifunctional Electrocatalysts for Rechargeable Zn-Air Batteries
Authors: Jun Li , Qiao Jin Li
Published: July 2021

Here, a bifunctional electocatalysts fabricated through a simple coprecipitation method on MOF precursor with micro/mesoporosity structure CoNi carbon nanotubes (Co/Ni/N-CNF). The as-prepared Co/Ni/N-CNF catalyst is essential to design and construct for enhancing the catalytic activity and vigorous durability simultaneously for ORR and OER. Significantly, the Co/Ni/N-CNF exhibits excellent oxygen reduction (ORR) electrocatalytic activity including onset potential (Eonset) and half-wave potential (E1/2) of 1.183 V and 0.82 V, which are comparable to commercial Pt/C-RuO2. Moreover, the constructed catalyst reveals lower operating voltage of 1.72 V at 10 mA cm−
2 (Ej=10), which is even superior to the commercial Pt/C-RuO2
. The signal activity can be ascribed to the synergetic effect between defect-riched N-doped carbon, porous structure and carbon nanotubes, which could induce notably dispersed active sites, superb conductivity, convenient electronic configuration, excellent durability and outstanding reaction pathways. Additionally, the catalyst with intelligent structure has a large surface area (269.703 m2 g−1), which is favourable for the exposure of catalytic active sites and mass transfer. This finding offers that developing the non-noble metal electrocatalyst to replace the noble metal electrocatalyst for practical applications of energy conversion and storage devices is possible.
Selective Electrochemical Reduction of CO2 By Cu-Bi Bimetallic Catalysts Grown on a Derived Copper Foamed Substrate
Authors: Lou Wenshuang , Qiao Jin Li
Published: July 2021

The effective conversion of CO2, a greenhouse gas, into high value-added products such as formate through electrochemical processes has been a key catalytic challenge under environmental conditions. There are many ways to improve the activity and selectivity of electrocatalytic CO2 reduction reaction (ECO2RR), and adjusting the geometry and electronic structure of the bimetallic electrocatalysts to facilitate specific reaction pathways and provide more active sites is one of the most promising methods. In this work, we demonstrate a significant correlation between the selectivity of CO2R to formate and the co-electrodeposition potential of Cu-Bi bimetallic catalysts on the derived copper foams. A Cu-Bi co-electrodeposition potential of -0.8V led to a cathode with a formate Faradaic efficiency of around 93% at -0.92 V vs RHE, which was more than 45% higher than the -0.5V co-electrodeposition cathode Faradaic efficiency (around 64%) under the same conditions. This result highlights the important role of the co-electrodeposition potential in the performance of Cu-Bi bimetallic catalyst CO2R grown on derived foamed copper substrate. Scanning electron microscopy (SEM) showed that the defects on the derived copper foams provided more sites for catalyst attachment, and the co-electrodeposition potential affected the particle size of Cu-Bi bimetallic catalyst.
Improved Ionic Conductivity of MgM4P6O24 (M = Hf, Zr) Ceramic Solid-State Electrolytes by Sol-Gel Synthesis
Authors: Adamu Mohammed , Kale Girish M
Published: July 2021

Noticeable improvements in the ionic conductivity of MgHf4P6O24 and MgZr4P6O24 solid-state electrolytes were measured on platinised pellets of 13 mm diameter and 3.8 mm thickness synthesised by the sol-gel method (presented in Figure 1) [1-4]. Electrochemical impedance spectroscopy deployed in this study, demonstrated and evaluated Mg2+-cation conducting species in the characterisation of MgHf4P6O24 and MgZr4P6O24 solid-state electrolytes using the two-probe analysis at a temperature range of 182 - 764 oC and 100 mHz - 32 MHz frequency range to determine the ionic conductivity data. In this study, a promising ionic conductivity of 4.52 x 10-4 Scm-1 and 7.23 x 10-3 Scm-1 for both MgHf4P6O24 and MgZr4P6O24 solid-state electrolytes, respectively, were evaluated at an impedance measurement temperature of 747 oC and 725 oC, respectively, while maintaining service stability of the highly sintered sample pellets at 1000oC ≤ T oC ≤ 1300. Meanwhile, the resultant pellets are believed to find useful applications as solid-state electrolytes in high-temperature electrochemical sensors, solid-state batteries and other electrochemical devices.

References

[1] M. Adamu, and G.M. Kale, The ECS Transactions,
98(12), 17-38 (2020)

[2] G.M. Kale, L. Wang, and Y. Hong, International Journal of Applied Ceramic Technology, 1(2), 180-187 (2004).

[3] M. Adamu, K.T. Jacob, and G.M. Kale, Journal of The Electrochemical Society,
167, 027532 (2020).

[4] M. Adamu, and G.M. Kale, The Journal of Physical Chemistry C,
120, 17909-17915 (2016).

Figure 1. Ionic conductivity of MgZr4P6O24 and MgHf4P6O24 solid-state electrolytes as a function of temperature

Figure 1
Instilling Monovalent Selectivity in Cation Exchange Membranes By Molecular Layer Deposition
Authors: Wormser Eyal , Nir Oded , Edri Eran
Published: July 2021

Desalination is becoming a vital part of the solution to water scarcity with a current worldwide desalination capacity of approx. 100 million m3/day, which is expected to grow by 40% by 2030. In 2019, 29% of the global desalination capacity was of brackish and river water (500-20000 ppm TDS). Most (98%) of the brackish water nowadays is desalinated by reverse osmosis (RO) which completely deprives the permeate of Mg2+ and Ca2+. Both are critical nutrients needed to sustain human health and agriculture. Replenishing these divalent ions to the desalinated water increases the cost and complexity of the overall process and decreases its sustainability and economic attractiveness. Electrodialysis is energetically more efficient than RO for desalination of brackish water, and using monovalent selective membranes—membranes that enable monovalent ions passage, but retains divalent ions—offer a potential solution to preserve the nutrients in the permeate. However, current methods for instilling ion selectivity uses large macromolecular building blocks to form the selective layer, which increases ion transport resistance and hence the energy demand and cost of selective electrodialysis. To disrupt the resistance-selectivity trade-off, a method for uniformly depositing an ultrathin and highly charged selective layer is needed.

While low-temperature atomic layer deposition is a suitable method for depositing ultrathin metal oxides on membranes, the elastic mismatch between metal oxides and polymers hinders the stability of the selective layer. Instead, we used molecular layer deposition of alucones to resolve the elastic mismatch. We show that the electrostatic charge of alucone surface leads to monovalent selectivity values on par with commercial membranes, but with only a marginal increase in resistivity.
High Ionic Conducting and Flexible Nasicon Membranes Enabled By Integrated Mechanical and Thermal Activation and Co-Sintering
Authors: Chiang Shan-Ju , Shaw Leon
Published: July 2021

NaSICON-type materials have been investigated since 70s and become an attractive candidate for energy storage and many other emerging applications due to their good ionic conductivity. However, further enhancement in ionic conductivity and mechanical flexibility at room temperature and facile processing methods to synthesize NaSICON in an energy efficient and low cost facet are required to enable various emerging applications. In this study, we report a novel processing method, termed integrated mechanical and thermal activation associated with co-sintering of stainless steel to address these challenges. It is found that Na3Zr2Si2PO12 membranes with little or no impurity, and total ionic conductivity of 1.53 × 10-3 S/cm at room temperature can be synthesized through one high-energy ball milling step followed by one high-temperature reaction, which significantly simplifies the synthesizing procedure for NaSICON membranes and achieves the high ionic conductivity. It is shown that further co-sintering of pure NaSICON and stainless steel has successfully increased the mechanical robustness of membrane while retaining good ionic conductivity reported in the literature. This study has provided a sturdy processing to synthesize high performance yet low cost NaSICON and NaSICON/stainless steel composite membranes that suitable for real world application.
Nanostructured Ruthenium-Titanium Oxides for Highly Active and Stable Oxygen Evolution Electrocatalysts
Authors: Godinez Salomon Jose Fernando , Rhodes Christopher P.
Published: July 2021

Proton-exchange membrane water electrolyzers produce high purity hydrogen from water and electricity and can be powered using renewable energy; however, the high material cost, limited global supply, and overpotential of iridium-based oxygen evolution reaction (OER) electrocatalysts result in high device costs (both up-front catalyst and input electricity costs). Ruthenium-based acidic OER catalysts have among the highest activities reported, which are higher than the activities of iridium-based catalysts. In addition, ruthenium has a significantly lower cost and higher global supply compared to iridium. Despite their advantages, ruthenium-based catalysts (both metallic and oxide forms) show higher degradation and less stability than iridium-based catalysts. Improving corrosion resistance while maintaining ruthenium activity is key to producing catalysts that are both highly active and long-lasting for clean hydrogen production via water electrolysis. To create highly active and stable acidic OER electrocatalysts, we have explored ruthenium-titanium oxide, Ru1-xTixOy, as a model system of the interaction of a highly stable and inactive metal (Ti) with a highly active, unstable metal (Ru) within an oxide structure. We evaluated different synthesis methods and thermal treatments to obtain ruthenium-titanium oxides with varied compositions and structures. The effect of altering the Ti ratio within ruthenium-titanium oxides on the structure and OER activity and stability were determined. Understanding how the interaction of active and inactive elements can influence the oxygen evolution reaction provides a pathway to develop electrocatalysts with higher activity, improved stable and lower cost.
Enhanced Photocatalytic Performance of Poly(3,4-ethylenedioxythiophene)- Coated TiO2 Nanotube Electrodes
Authors: Abdelnasser Shady , Park Geunsu , Han Hyunwoo , Toth Rita , Yoon Hyeonseok
Published: July 2021

This study presents the design of a mixed organic–inorganic system to be utilized in solar-light chemical energy conversion applications, where the visible-light absorption properties of the conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), are combined with the enhanced charge transport properties of TiO2 nanotubes, thus creating an efficient photoelectrode. A dispersion of PEDOT doped with p-toluenesulfonate (tosylate) ions was synthesized using a simple solution-casting polymerization process, which was then spin-coated onto an ordered array of anodically fabricated TiO2 nanotubes to be used for solar energy conversion. Electron microscopy observation confirmed the presence of PEDOT in the hybrid (PEDOT–TiO2) and Fourier transform infrared spectroscopy verified the vibrational modes of the polymerized PEDOT. The ultraviolet-visible diffuse reflectance data indicated a change in the absorption edge of the pure TiO2 nanotubes to longer wavelengths after PEDOT coating. The developed photo-electrodes exhibited a significant increase in photocurrent response and lower charge transfer resistance with respect to the pure TiO2 nanotubes, as verified by electrochemical impedance spectroscopy.
Finding Point of Zero Charge Using Phase-Sensitive Second-Harmonic Generation
Authors: Xu Pengtao , Suntivich Jin
Published: July 2021

We present how to use phase-sensitive second-harmonic generation (PS-SHG) to identify the point of zero charge of an electrochemical interface. The electrical double layer plays an essential role in hydrogen and oxygen electrocatalysis. Yet, very little is known about the interfacial electric field. Second-order nonlinear spectroscopy such as SHG can provide interface-specific information. In this contribution, we will show how the SHG phase can reveal information about the interfacial electric field. Our PS-SHG measurement indicates that the SHG response of a platinum-water interface follows the parabolic model. We can use this analysis to obtain the point of zero charge on platinum and discuss the implication of the finding on our fundamental understanding of electrocatalysis.
Mesoscale Control of PGM Electrocatalysts Using Self-Assembled Block Copolymer Templates
Authors: Bhattacharya Deepra , Arges Christopher G.
Published: July 2021

Platinum Group Metals (PGMs) are state-of-the-art electrocatalysts for electrochemical energy conversion technologies. This talk presents a templating approach for the fabrication of dense and periodic platinum and iridium oxide nanowires and standing cylinders with tuned feature sizes (e.g., 12 to 40 nm) and long-range order from self-assembled block copolymer thin films. Unlike previous studies, we show that a starting template utilizing an ion-containing block copolymer electrolyte over a non-ionic block copolymer yields thicker and denser metal/metal oxide nanostructures. PGM geometry and chemical composition were characterized using electron microscopy, atomic force microscopy, grazing incidence x-ray scattering, x-ray photoelectron spectroscopy, and inductively coupled plasma – optical emission spectrometry. The structural characterization tools show high-fidelity pattern transfer from the block copolymer template to the PGM nanostructure. Additionally, the templating process was conducive for preparing the nanostructured PGMs on glassy carbon disks and interdigitated electrodes (IDEs) for electrochemical reactivity assessments. The former substrates were used to assess HER and ORR in a conventional rotating disk electrode setup, while the latter platform was amenable for hydrogen pump and water electrolysis demonstrations with thin film low-temperature and high-temperature polymer electrolytes. Electrochemical measurements revealed a commensurate trend between PGM surface area and mass activity. In summary, the block copolymer templating approach represents a unique platform for high throughput comparative analyses of the intrinsic catalytic activity as a function of meso-scale geometry. It is also an effective platform to understand electrocatalytic reactivity differences for a given catalyst with different types of electrolytes.
Tuning the Composition of Silicon Oxide Overlayers to Control the Performance of Platinum Electrocatalysts
Authors: Beatty Marissa , Esposito Daniel V. , Gillette Eleanor , Haley Alexis T.
Published: July 2021

Membrane coated electrocatalysts (MCECs) have shown to be an attractive approach for improving the activity, stability, and selectivity of various electrochemical reactions. However, little is known about how overlayer structure impacts different catalytic properties and ultimate performance. By analyzing the affect that overlayer composition has on the electrochemical behavior for various probe reactions, guiding relationships that correlate MCEC structure and performance can be derived. For a silicon oxide (SiOx)|Pt MCEC, limiting the conversion of polydimethyl-siloxane (PDMS) to SiOx during synthesis can result in varied concentrations of carbon in the overlayer film, allowing composition to be manipulated and studied directly. These changes in composition consequently affect the hydrophobicity, density, and silicon-oxygen coordination of the overlayer, which in turn influences the final transport behavior of the SiOx membrane. Specifically, platinum electrodes with partially converted SiOxCy overlayers demonstrate a decreased permeability for protons when studying the hydrogen evolution reaction (HER), compared to the less carbon rich, fully converted Pt|SiOx electrodes. Surprisingly, the opposite trend was observed for oxygen permeability during the acidic oxygen reduction reaction (ORR), where the fully cured overlayers free of carbon suppress the transport of oxygen to the buried interface. These contrasting trends in transport suppression present a unique opportunity for future designs to dial in specific, intermediate concentrations of common co-reactants like oxygen and protons, potentially allowing for increased selectivity, poisoning resistance, and stability of the underlying catalyst simply by altering the overlayer’s final composition. Collectively, these results demonstrate the broadened design space that MCEC-style electrocatalysts introduce for future electrochemical systems, and further extend their applicability and relevance to a broader range of reactions.
Chromium Nitride/ N-Doped Carbon Heterostructure As Oxygen Reduction Electrocatalyst
Authors: Sarkar Bidushi , Nanda Karuna Kar
Published: July 2021

One of the major challenges for the widespread application of clean energy technologies like fuel cells and metal air batteries is the development of an efficient Pt-free electrocatalyst for the cathodic oxygen reduction reaction (ORR). Further, the ORR activity is largely dependent on the pH of the electrolyte. To use a single catalyst for anion exchange membrane fuel cell, cation exchange membrane fuel cells and direct methanol fuel cells, the catalyst should be ORR active in alkaline as well as in acidic media and should be methanol tolerant.

In this regard, we synthesised chromium nitride (CrN) nanoparticles anchored onto N-doped graphitic carbon (CrN@NG) as a wide pH ORR catalyst active in alkaline as well as acidic media. The synthetic route offers a drastic development over traditionally used methods like nitridation, nanopatterning, etc by omitting the use of toxic ammonia and any expensive machinery. The CrN@NG catalyst is synthesized using simple precursors using single step pyrolysis. The CrN catalysts are reported to be used as ORR catalyst in alkaline media but the usage in acidic media is still restricted. Herein, the CrN@NG catalyst can potentially replacw Pt/C catalyst in alkaline and acidic media with comparable E1/2, Eonset and better durability. The close adherence of CrN nanoparticles and NG support plays a major role in enhancing the ORR activity. We believe that the simplistic method reported can be expanded to other metal nitrides as well.
(Invited) Modeling Non-Steady-State Membrane Transport in Operating Solar Fuels Systems
Authors: Houle Frances
Published: July 2021

Membranes are key components in both liquid electrolyte and vapor fed solar fuel generators, blocking product crossover between cathodic and anodic regions while permitting charged species to be transported. The internal and external environments of membranes are not at steady state in use, however, which can dynamically influence their permeability to neutral and charged species. In this talk, some time-dependent aspects of membrane characteristics as revealed by computational-experimental investigations will be described. These include relaxations due to gas sorption in glasses, membrane permeability to CO2 reduction products during a diurnal cycle, and water losses in use because of evaporation. The computational models resulting from these studies are predictive, and provide insights that may assist with the design and optimization of solar fuels systems with stable performance.
(Invited) Potentials and Challenges of Wide Bandgap Copper Chalcopyrite Thin Film Absorbers for Photoelectrochemical Water Splitting Applications
Authors: Gaillard Nicolas
Published: July 2021

Photoelectrochemical (PEC) water splitting has the potential to become an efficient method for renewable hydrogen production. However, the efficiency, projected cost, and durability of lab-scale systems are not yet at the level required to make this technology economically feasible. Amongst all materials studied to date, the chalcopyrite class is arguably one of the best classes for PEC water splitting, as it has already demonstrated low-cost and high photoconversion capabilities as a photovoltaic material. In the context of PEC, our group has shown that co-evaporated 1.65 eV bandgap (EG) CuGaSe2 is capable of evolving hydrogen with Faradaic efficiency greater than 85% and generate photocurrent densities over 15 mA.cm-2, as measured in a 3-electrode configuration in 0.5M H2SO4 under simulated AM1.5G illumination. Unfortunately, CuGaSe2’s narrow EG limits its integration as top absorber into a dual junction stacked PEC device (also known as hybrid photoelectrode, HPE). In the present communication, we report on our latest efforts to synthesize wide-EG (1.8-2.0 eV) chalcopyrites, compatible with the HPE integration scheme, and capable of generating saturated photocurrent densities greater than 10 mA/cm2. We present specifically results on EG tunable Cu(In,Ga)(S,Se)2, Cu(In,Ga)S2, CuGa(S,Se)2 and CuGa3Se5. We also discuss some of the strategies developed to improve their surface energetics for the hydrogen evolution reaction, including the use of bandgap tunable MgZnO n-type buffer layers. We also include recent durability testing of chalcopyrite photocathodes coated with metal oxide protection layers. Finally, we present solid-state techniques and theoretical modeling used by our team to identify possible pitfalls in these material systems and discuss potential paths for improvement.
Effects of Effluent Stream Composition and Competing Reactions Effect on Wastewater Nitrate Reduction in a Photoelectrochemical Device
Authors: Barrera Luisa , Bala Chandran Rohini
Published: July 2021

More than 80% of nitrogen-contaminants are present in the form of nitrates in point sources of wastewater, including municipal wastewater effluents, ion-exchange brines, low-level nuclear wastes and in power generation. Wastewater nitrates represent an untapped source for the recovery of nutrients, value-added chemicals, and energy. Nitrates can be reduced to form ammonia, which can be used as a fertilizer or fuel, and nitrous oxide, which is a powerful oxidizer for the combustion and supercharging applications. Depending upon the source of the wastewater, the concentration of nitrates present in these streams can vary significantly. Ion-exchange brines and low-level nuclear wastes have large nitrate concentrations, on the order of > 0.1 M, whereas municipal and power generation effluents are more dilute (0.1 mM). However, the effect of varying contaminant concentrations and the competing redox reactions have not been quantified for these systems.

In this study, a photoelectrochemical device is proposed to transform wastewater nitrates into ammonia, coupled with water oxidation. We expand on a previously developed numerical model to include the effects of the reacting nitrate species concentrations and the competing redox reactions on the solar-to-chemical efficiencies and nitrogen-removal rates. Notably, we implemented an equivalent circuit modeling approach to account for the influences of the competing reactions and the concentration-dependent mass-transfer limiting current densities. Model results predict that for a single light-absorber and a nitrate concentration of 100 mM, the optimal solar-to-chemical efficiency is 7% and the nitrogen recovery rate (as NH3) is 260 gN m-2 day-1. Oxygen reduction is more dominant as a competing reaction than hydrogen reduction at the cathode. However, this reduction is mass-transfer limited even while assuming an air-saturated (1 atm) device and therefore didn’t impact the performance significantly. Modeling results are complemented by experimental measurements of the effects of nitrate concentrations on the operating current densities and the rates of product formation with copper and platinum electrodes at the cathode and anode respectively.
Visible to Near-Infrared Light Photocatalytic Nitrogen Fixation on Bismuth Oxyiodide Nanosheets without Sacrificial Reagents
Authors: Mohebinia Mohammadjavad , Wu Chunzheng , Yang Guang , Dai Shenyu , Hakimian Alireza , Tong Tian , Ghasemi Hadi , Wang Zhiming , Wang Dezhi , Ren Zhifeng , Bao Jiming
Published: July 2021

As an essential feedstock for fertilizer and chemical industries, ammonia is being produced by a so-called Haber-Bosch process. However, global warming and the energy crisis urge us to find a sustainable and clean alternative for ammonia production. Photocatalytic nitrogen fixation is an alternative but challenging method. Low reactivity of nitrogen molecules, slow production rate, poor light-absorption capacity, and need of using organic sacrificial chemicals are the most pronounced challenges of the photocatalytic nitrogen fixation process. Among previously studied photocatalysts, bismuth oxyiodide (BiOI) is an excellent candidate due to its full visible-light absorption and nitrogen binding affinity. However, BiOI is suffering from its positive conduction band minimum potential, which is lower than the proton-assisted nitrogen reduction potential (-0.23 eV vs. RHE). In this talk, I will show that the surface electric dipole induced by PVP molecules on BiOI nanosheets upshifted the band edge potentials, thus enabling redox reactions simultaneously.
(Invited) A Synthetic Catalyst for the Electrocatalytic Conversion between CO2 and HCO2-
Authors: Cunningham Drew , Yang Jenny Y
Published: July 2021

Reversible catalysis is a hallmark of energy‐efficient chemical transformations, but can only be achieved if the changes in free energy of intermediate steps are minimized and the catalytic cycle is devoid of high transition‐state barriers. Using these criteria, we demonstrate reversible CO2/HCO2
− conversion catalyzed by [Pt(depe)2]2+ (depe=1,2‐bis(diethylphosphino)ethane). Direct measurement of the free energies associated with each catalytic step correctly predicts a slight bias towards CO2 reduction. We demonstrate how the experimentally measured free energy of each step directly contributes to the <50 mV overpotential. We also find that for CO2 reduction, H2 evolution is negligible and the Faradaic efficiency for HCO2
− production is nearly quantitative. A free-energy analysis reveals H2 evolution is endergonic, providing a thermodynamic basis for highly selective CO2 reduction.
(Invited) Multi-Scale Photocorrosion Modeling in Photoelectrodes and Photoelectrochemical Devices
Authors: Haussener Sophia
Published: July 2021

The development of a sustainable energy economy based on renewable, carbon-neutral energy is a necessary and urgent task. Photo-electrochemical (PEC) approaches to solar fuels and materials are interesting, provided they can be efficiently, stably, scalably, and sustainably implemented.

While significant progress on the development of earth abundant materials and on high-efficiency demonstrations has been achieved, there is relatively little known about the behavior of materials and devices under more realistic, varying conditions and on the implication of degradation on the performance and lifetime.

Here, I will first discuss multi-scale numerical modeling approaches to investigate and quantify the effect of photocorrosion on the performance evolution. I will show how important the local reaction environment is for the stability of a component, and how heterogeneity in the operating variables (current density, species concentration, temperature, etc.) affect degradation. Furthermore, I will comment on the importance of device design on device stability.

Second, I will then transition towards discussing material, device and system performance as a function of varying, non-design-point operation. I will show how these dynamics can affect the performance, show how multi-physical transport can help in controlling and smoothing some of the observed variations, and generally highlight synergistic effects. I will end with providing general guidelines on operating materials, devices and systems under more realistic conditions.
An Unbranched, Hybrid Conductive-Redox Polymer for Interfacing Intact Chloroplasts and Electrode Surfaces during Photobioelectrocatalysis
Authors: Weliwatte Nipunika Samali , Grattieri Matteo , Minteer Shelley
Published: July 2021

Photobioelectrocatalysis (PBEC) adopts the sophistication of photosynthetic units, their abundant availability, easy processing and sustainability, to convert solar energy into electricity. Specifically, the use of chloroplasts as photobioelectrocatalysts is desirable due to their metabolic independence and photoprotection mechanisms. However, the protein-based outer membranes of chloroplasts impede efficient charge transfer onto electrode surfaces during PBEC. Typical bio-inspired redox polymers used to ameliorate this charge transfer are branched, and contain redox pendants peripherally attached to a backbone. Pendants extract, and propagate electrons via collision-based electron tunneling. Conversely, we investigate the ability of an unbranched hybrid conductive-redox polymer, polydihydroxy aniline (PDHA), which has its redox moiety embedded in a conductive backbone. The redox moiety of PDHA is a quinone derivative, with redox potentials higher than the quinone-based redox active sites of chloroplasts. The biohybrid chloroplast-PDHA electrode encapsulates chloroplasts in a conductive matrix of PDHA, improving charge transfer. Holistically, PDHA facilitates the immobilization of chloroplasts and mediate electron transfer between chloroplasts and electrode surfaces. Our results demonstrate that a 120 % photocurrent increment is obtained upon combining chloroplasts with PDHA. Sequentially layering chloroplasts and PDHA on electrode surfaces evinces a 260 % increment in photocurrent responses. We report the highest photocurrent recorded with chloroplasts during PBEC (-48±3 µA cm-2) by pairing chloroplast-PDHA electrodes with diffusible redox mediator, 2,6-dichlorobenzoquinone. The study shows that redox polymer designs for artificially mediating electron transfer from chloroplasts can extend to unbranched conductive polymers in PBEC systems.

Figure 1
Modeling Photocatalysts and Reactors for Solar Hydrogen Production through Particle-Based Water Splitting
Authors: Savant Sangram Ashok , Haussener Sophia
Published: July 2021

Hydrogen as an energy carrier has by far the highest gravimetric energy density, which, when produced by a renewable pathway would go a long in achieving the goal of carbon neutral and responsible economy. Photocatalytic water splitting is a promising approach for the production of solar hydrogen. The technological potential of this approach is unclear and it is not known how the choice of the components (semiconducting particles, electrolyte, mediator, etc.), the design of the system, and the operating conditions affect the performance of the system.

Firstly, we present a steady 1-dimensional model of a single photocatalyst particle which couples semiconductor physics to account for the charge carrier generation and transport with the electrochemical kinetics governed by the butler-volmer equation. We account for the solar absorption and the charge carrier generation with Lambert-Beer’s law. We then solve for the carrier transport and conservation with Poisson’s equations and the hole and electron transport by drift diffusion currents. We assume the recombination in the particle to be a Shockley-Reed-Hall trap recombination. The semiconductor electrolyte interface is treated as an ideal Schottky contact. We show the effect of intrinsic parameters like doping concentration, electron affinity (band positions), relative permittivity on the operating current density. We also present the effect of particle size on the operating current density.

Secondly, we present a transient 0-dimensional model, which accounts for ideal solar absorption, ideal charge generation and transport, and the kinetic characteristics at the catalytic sites for two sets of photocatalyst semiconductor particles. We solve for species transport (mediator species and protons) and conservation in the one or two reactor compartments separated by a semipermeable membrane. We evaluate this 0-dimensional model on a reactor level as well, comparing three different reactor types, these three types include: i) a single photocatalyst reactor, ii) a membrane-separated dual compartment reactor and iii) a membrane-separated dual compartment reactor with wire and two auxiliary electrodes. We put forth a theoretically limiting efficiency which considers no overpotentials and a realistic case which accounts for losses for each type of reactor. For these reactor designs, we establish a link between the thermodynamic limits and materials requirements, changes in material requirements when more realistic operation and losses are considered, and compare the three reactor designs.

Conclusively, the steady 1-dimensional particle model allows us to evaluate the effect of intrinsic material properties of a single photocatalyst on the operating current density, and the transient 0-dimensional model giving us a broader evaluation on a reactor design level with respect to the employed photocatalysts and redox mediators.