bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Modification of TiO2 with Metal Oxides for Water Splitting
Authors: Nolan Michael , Rhatigan Stephen 
Published: July 2021

The photocatalytic oxidation of water to molecular oxygen is a key step in the water splitting reaction. The development of robust catalysts with high efficiency in this half-reaction is crucial for achieving technological application of water splitting. Density functional theory studies predict that alkaline earth metal oxide modified TiO2 can enhance water activation and the free energies of oxygen evolution reaction (OER).
DFT simulations were performed on extended rutile (110) and anatase (101) surfaces modified with alkaline earth oxide (AEO) nanoclusters of composition (MO)4 and (MO)12 to explore coverage and dispersion effects in the nanocluster modification of TiO2
1. We use the VASP5.4 code with a cut off energy of 400 eV, the PW91 approximation to the exchange-correlation functional and the DFT+U approach to describe the partially occupied 3d states in reduced TiO2, with U = 4.5 eV.
We use models of rutile (110) modified with MgO nanoclusters of composition (MgO)4 and (MgO)12 to model dispersion/coverage effects. The nanoclusters bind strongly the rutile surface, forming new interfacial bonds. Computed formation energies of oxygen vacancies show that these heterostructures are easily reducible, with reductions of ca. 2 eV in the cost of forming oxygen vacancies, with electron localization on the TiO2 substrate. The computed free energy for the OER steps , using the standard computational model for structures without and with surface hydroxyls shows that moderating stability of the *OH intermediate in the water oxidation steps, reduces the overpotential compared to pure rutile (110) and competitive with hematite. The most favourable water adsorption mode for OER is at the MgO-rutile interface.
Work on other surface modified TiO2 materials includes CeO2 and MnOx, where these are also reducible and activate water to produce hydroxyls. Comparison is made with experimental results from collaborators.
High Performance Low PGM Alkaline Membrane Water Electrolysis
Authors: Strasser Derek James , Xu Hui , Kabir Sadia , Shi Wenjuan , Rojas-Carbonell Santiago , Yan Yushan , Wu Gang , Shi Qiurong 
Published: July 2021

Development of water electrolysis technology is critical to the future of clean energy consumption and storage. Alkaline membrane water electrolysis is very attractive owing to the high energy density of the hydrogen produced and, more importantly, the possibility of lowering system cost by significantly lowering or completely replacing platinum group metal (PGM) catalysts with less expensive metals such as nickel and iron. Replacing perfluorinated membranes with much less expensive hydrocarbon based materials such as oxidation-resistant alkaline membranes and ionomer that are stable under water electrolysis operating conditions will also improve system costs and durability requirements. Previous research has focused on alkaline electrolyzers operating with KOH supporting electrolyte.1 To date, it is clear that alkaline membrane electrolysis is still low technology readiness leveltechnology with reported limitations such as membrane/ionomer durability, non-PGM catalyst performance and durability and previously mentioned, operation with a supporting electrolyte, such as KOH to achieve performance, which adds significant cost to design a corrosion resistant device.
In this study, we have developed an alkaline membrane water electrolyzer which operates with pure water and employs non-PGM anode catalyst. Initial focus was to demonstrate membrane and ionomer performance and durability during electrolyzer operation without the use of added electrolyte. We have demonstrated for the first time 500 hours of cell operation with pure water at 500 mA/cm2 and a cell potential of 1.7 V using standard PGM catalysts indicating significant durability. Replacing the iridium oxide with PGM-free catalyst and operating the electrolyzer with pure water will lead to significant cost saving both in catalyst materials and allow for less expensive stainless-steel current collectors. More recently, an alkaline water electrolyzer with iron and nickle based PGM-free based anode catalysts has demonstrated promising performance while operating on pure water.
Reference

Abbasi, R., Setzler, B. P., Lin, S., Wang, J., Zhao, Y., Xu, H., Pivovar, B., Tian, B., Chen, X., Wu, G., Yan, Y., A Roadmap to Low‐Cost Hydrogen with Hydroxide Exchange Membrane Electrolyzers. Mater.2019, 31, 1805876
(Invited) High-Temperature Alkaline Water Electrolysis Using Composite Ceramic-Molten Hydroxide Membrane
Authors: Lattimer Judith , Xu Hui , McCatty Steve , Mohan Yamini , Singh Prabhakar , Rahman Muhammad Anisur , Aphale Ashish 
Published: July 2021

Hydrogen production from water electrolysis for mobile and energy storage applications is attractive due to its high efficiency, fast ramp rates, and potential for the clean energy economy. However, current hydrogen production from electrolysis comprises only a small fraction of the global hydrogen market due to the high cost associated with expensive stack materials (membrane, catalyst, and bipolar plates) and electricity consumption of the commercial electrolysis systems. We have developed a high temperature alkaline electrolyte-based water electrolyzer (HTAWE) that operates at 350-550 °C, enabling high reaction rates while limiting thermal degradation compared to solid oxide cells operating above 700 °C. This water electrolyzer is based on our innovative molten hydroxide electrolyte impregnated in a porous ceramic matrix, which has conductivity as high as 0.4 S/cm at 350 °C, enabling rapid hydroxide transport. This HTAWE can simultaneously reduce the electrolyzer cost (by adopting cheap material) and improve energy efficiency (by enabling high-temperature operation).
Using an innovative new SrZrO3-based matrix, we have demonstrated exceptional water electrolysis performance using both single and binary hydroxide mixtures. We successfully achieved sustained cell performance of 1.35 V at a current density of 1,000 mA/cm2 with area specific resistance (ASR) 0.1 Ohm-cm2 across the cell at furnace temperature 500 °C. We were also able to demonstrate cell performance of 1.45 V at a current density of 1,000 mA/cm2 with ASR of <0.2 Ohm-cm2 across the cell at a furnace temperature 400 °C. Furthermore, we have demonstrated stable cell performance for >1000 h of continuous operation at 1 A/cm2 with ASR of 0.2 Ohm∙cm2 across the cell.
(Invited) Membrane Coated Electrocatalysts for Seawater Electrolysis
Authors: Baxter Amanda F. , Beatty Marissa , Bhardwaj Amar , Esposito Daniel V. 
Published: July 2021

One obstacle to the widespread adoption of water electrolysis powered by renewable sources is the availability of highly pure water required by conventional electrolyzers. This is particularly true for hot, dry coastal regions which have access to seawater and great potential for harvesting solar and wind energy, but where fresh water is often scarce. Additionally, seawater makes up 97% of the water on Earth, and although desalination is possible, it adds cost to the electrolysis system. Thus, direct seawater electrolysis could be a more cost effective approach to hydrogen production that doesn’t strain fresh water resources. However, direct seawater electrolysis is challenging due to the large concentration of Cl- ions, which can be detrimental to electrocatalyst stability and is a reactant for the undesirable chlorine evolution reaction (CER) that competes with the oxygen evolution reaction (OER) at the anode. Mitigating the CER is important because Cl2 is toxic and harmful to the environment.
Our group has shown that ultrathin semi permeable oxide overlayers can be designed to modulate transport of reactants to the active catalyst at the buried interface. Thus, the oxide overlayer acts as a membrane, rendering the material a membrane coated electrocatalyst (MCEC). An additional advantage of the MCEC architecture compared to conventional electrocatalysts is enhanced stability. The overlayer can act as a glue holding catalyst particles in place, which we have shown comparing SEM images before and after chronoamperometry in 0.6 M NaCl. This work describes how MCECs can be applied to seawater electrolysis to i) improve catalyst stability and ii) enable selectivity for OER over CER by impeding transport of Cl- ions to the buried interface.
Carbon Nanostructures-Transition Metal Oxide Hybrid As Bifunctional Electrocatalyst
Authors: Devi Hemam Rachna , Bisen Omeshwari Yadorao , Chen Zhong , Nanda Karuna Kar 
Published: July 2021

The keen to replace coal and petroleum-based energy with renewable and environment friendly resources has persuaded the research in energy conversion and storage devices like metal-air batteries, fuel cell and electrolyzers. Oxygen electrochemistry that includes oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are sluggish reactions. RuO2/IrO2 and Pt-C are promising candidates in terms of the catalytic performance for OER and ORR, respectively. However, stability and the cost hinder its usage for large scale commercial applications. Therefore, rational designing of electrocatalyst that can overcome these sluggish reactions accounting their economic factor is important. Moreover, designing bifunctional catalyst remains a challenging issue till now. Carbon based materials have been extensively known for ORR whereas transition metal oxides show promising OER. 1
2 In this regard, we have synthesized a hybrid consisting of one-dimensional carbon nanostructures supported on Co-Ni oxide that shows efficient OER and ORR activity with low overpotential (OER), E1/2 (ORR), excellent stability and durability. The low Tafel slope for both OER and ORR reveals favorable reaction kinetics. Importantly, the hybrid offers ∆E (Ej=10 -E½) of 0.80 V that shows the promising bifunctional behavior. The overall study indicates that the hybrid catalyst is as potential candidate for OER/ORR and hence, expected to serve the energy storage device like metal-air batteries.

References

(1) Devi, H. R.; Nandan, R.; Nanda, K. K. Mechanistic Investigation into Efficient Water Oxidation by Co-Ni-Based Hybrid Oxide-Hydroxide Flowers. ACS Appl. Mater. Interfaces
2020, 12 (12), 13888–13895.
(2) Nandan, R.; Devi, H. R.; Kumar, R.; Singh, A. K.; Srivastava, C.; Nanda, K. K. Inner Sphere Electron Transfer Promotion on Homogeneously Dispersed Fe-N XCenters for Energy-Efficient Oxygen Reduction Reaction. ACS Appl. Mater. Interfaces
2020, 12 (32), 36026–36039.
(Invited) Photo-Electrochemical Hydrogen Production Systems Using III-V Semiconductors: Challenges in Scaling-up from an Electrode to a Device
Authors: Deutsch Todd G , Young James , Klein Walter , Steiner Myles 
Published: July 2021

While III-V semiconductors have achieved the highest photo-electrochemical solar-to-hydrogen conversion efficiencies, they are remarkably unstable during operation in a harsh electrolyte. The first part of this talk will focus on the degradation mechanism of inverted metamorphic mulijunction (IMM) III-V cells and surface modification strategies aimed at protecting them from photocorrosion. We applied noble metal catalysts, oxide coatings by atomic layer deposition, and MoS2 in an effort to protect the GaInP2 surface that was in contact with acidic electrolyte. We also grew epitaxial capping layers from III-V alloys that should be more intrinsically stable than GaInP2. The ability of the various modifications to protect the IMM’s surface was evaluated by operating at each electrode at short circuit for extended periods of time.
The second part of this talk will identify the challenges encountered while scaling the IMM III-V absorber areas of from ~0.15 cm2 up to 16 cm2 and incorporating them in a photoreactor capable of generating 3 standard liters of hydrogen in 8 hours under natural sunlight. To successfully scale photo-electrochemical water-splitting technologies from bench to demonstration size requires addressing predictable and unpredictable complications. Despite using Comsol multiphysics to model our photoreactor and identify suitable specifications for a prototype, several practical issues were uncovered during testing that led to multiple iterations of photoreactor design between the initial and final generations. Several bottlenecks that ranged from counter electrode composition and orientation to bubble management needed redress in order to meet our performance targets. Ultimately, the demonstration-scale system was able to generate nearly twice the target volume of hydrogen in an 8-hour outdoor trial.
(Invited) Understanding Multi-Component Transport and Reaction Phenomena in Bipolar Membranes Used for Electrosynthesis
Authors: Bui Justin C. , Bell Alexis T. , Weber Adam Z. 
Published: July 2021

Bipolar membranes (BPMs), which have long seen usage in electrodialysis reactors for the generation of acid and base, have recently demonstrated potential to become critical components in electrochemical synthesis devices. Because they can operate under large pH gradients, BPMs enable favorable environments for electrocatalysis at the individual electrodes. Critical to the implementation of BPMs in these devices is understanding the kinetics of water dissociation that occurs within the BPM junction as well as the co- and counter-ion crossover through the BPM, which both present significant obstacles to developing efficient and stable BPM-devices for electrosynthesis applications. Prior work has modeled ion transport in bipolar membranes in neutral salt solutions for electrodialysis. However, no model exists for the BPM under the harsh applied pH gradients that would be present in electrosynthesis, and there is significant need to explore the effects of the internal hydration on the lifetime and performance of BPMs in such environments. Additionally, a mechanistic understanding of water dissociation catalysis will be required to develop interfacial catalysts that enable the high current density operation required for scalable electrosynthesis of fuels.
In this talk, we discuss modeling methodologies and physics inherent in BPMs and present our recent model of ion transport and water dissociation catalysis in BPMs across the pH scale. Specifically, we simulate multi-ion transport for a BPM with various electrolyte combinations on each side of the membrane, demonstrating the significance of co- and counter-ion crossover in BPMs operating under harsh pH gradients. We then investigate effects caused by hydration gradients that occur due to internal ion-exchange and examine potential methods for improving performance and mitigating crossover. Finally, we examine the impact of the interfacial water dissociation catalyst and perform sensitivity analysis on the key properties (catalyst point of zero charge and pKa) that dictate catalyst performance. These results provide information that is critical to developing a comprehensive understanding of multi-component phenomena in BPMs and to informing the design and implementation of BPMs in next-generation devices for the numerous electrosynthesis chemistries that benefit from operation under an applied pH gradient.
(Invited) Dye-Sensitized Oxide Nanosheets for Visible-Light Water Splitting
Authors: Maeda Kazuhiko 
Published: July 2021

Metal oxide nanosheets derived from the layered counterparts have attracted attention in various fields due to their unique structural properties. The anisotropic feature of nanosheets, having a thickness of ~1 nm and lateral dimensions ranging from several hundred nanometers to a few micrometer, is advantageous for heterogeneous photocatalysis, as the diffusion length of photogenerated carriers to the surface is shortened, leading to higher activity.
It is also known that certain nanoparticulate metals or metal oxides on a semiconductor photocatalyst work as cocatalysts to promote water reduction and/or oxidation. In heterogeneous photocatalysis, the effect of cocatalyst size on the water-splitting performance had not been examined at sizes smaller than 1 nm due to the lack of an effective preparation method and a suitable photocatalyst. We have demonstrated that metal nanoclusters (such as Pt) of <1 nm in size could be deposited on the interlayer nanospace of KCa2Nb3O10 using the electrostatic attraction between a cationic metal complex and a negatively charged Ca2Nb3O10
– sheet, without the aid of any additional reagent. The material obtained exhibited 8 times greater photocatalytic activity for overall water splitting under band-gap irradiation than the previously reported analog using a RuO2 promoter. This study highlighted the superior functionality of <1 nm Pt nanoclusters for photocatalytic overall water splitting.
With further modification by a ruthenium(II) photosensitizer, this material also worked as a H2 evolution photocatalyst in visible-light-driven Z-scheme water splitting, in combination with a WO3-based O2 evolution photocatalyst and a triiodide/iodide redox couple. Pt-intercalated HCa2Nb3O10 nanosheets further modified with amorphous AlO
x
clusters demonstrated a remarkable photocatalytic activity with a dye-based turnover number and frequency for H2 evolution of 4580 and 1960 h–1, respectively, which were by far the highest among dye-sensitized nonsacrificial photocatalytic systems ever reported.
(Invited) Enable Efficient Solar Driven CO2 Reduction with Stable and Highly Active Oxygen Evolution Catalyst in Neutral pH
Authors: Jia Hongfei , Zhou Li , Chen Ling 
Published: July 2021

Using electricity generated from solar cells, conversion of water and CO2 to syngas in an electrolytic cell mimics the photosynthesis process and provides a facile pathway to the production of various chemicals and liquid fuels.1 Development of new oxygen evolution reaction (OER) catalysts that are both active and stable in neutral pH is highly desired for such a process to avoid the complication of managing the pH gap between CO2 reduction on the cathode and water oxidation on the anode. Over the last several years, we have investigated various transition metal oxides as potential candidates for OER for artificial photosynthesis, including CoWO4, Li2CoGeO4 and various perovskites.2-4 It has been revealed that these catalysts were not stable in neutral pH and subjected to degradation either thermodynamically or kinetically.
In this presentation, we report a new brownmillerite OER catalyst, Sr2GaCoO5 (SGC), with superior performance and durability. At pH 7.0, the catalyst has a specific activity about 7.8-18.3 times higher than that of IrO2 at the applied electrode potentials between 1.53-1.73 V vs. RHE. With a catalyst loading of 1 mg/cm2, the measured overpotential was only 0.38 V at a current density of 10 mA/cm2, which maintained unchanged over the testing period of 72 hrs. A comparative study against Sr2AlCoO5 indicates the excellent stability of SGC is related to the presence of gallium oxide in the crystal structure, which may help prevent SGC from dissolution under the OER operation condition in neutral pH, although detailed mechanistic understanding should be further developed by additional studies in the future. Combining this novel OER catalyst with an anodized silver cathode and a triple junction of GaInP/GaInAs/Ge photovoltaic, the CO2 reduction system demonstrated a solar-to-CO energy conversion efficiency of 13.9% over a period of 19 hrs with no appreciable performance degradation.5 This result has shown that artificial photosynthesis can indeed be more efficient than the natural photosynthesis process for CO2 reduction, and should play an important role in addressing the challenges of global warming and climate change.
References:

Chem. Commun. 51, 17704–17707 (2015)

RSC Adv.
2(29), 10874-10881 (2012)

Mater. Chem. A. 2(43): 18428-18434 (2014)

Chem. Chem. Phys., 17, 22576-22580 (2015).

Nat. Commun. 10
, 4081 (2019)
Electrochemical Nitrogen Reduction Reaction over Subnano-Clustered Ruthenium Catalysts: A DFT Study
Authors: Kim Seung-hoon , Yoo Geunsang 
Published: July 2021

The electrochemical nitrogen reduction reaction (NRR) for ammonia production is one of the most spotlighted chemical process for hydrogen storage and transportation. We investigated NRR on the ruthenium-based subnano-clustered catalysts embedded in modified defective graphene (Rux/YC, Ru : ruthenium, x : 1 to 3, Y : boron, carbon, and nitrogen, C : graphitic carbon) using density functional theory (DFT) calculation.
We identified the energetically optimized structures of Rux/YCs among all possible geometries. Also we calculated the dissociative adsorption free energy of nitrogen (ΔGDiss) to determine which mechanism to follow for NRR on Rux/YCs. We also calculated the adsorption energy (ΔEAds) of all possible reaction intermediates to identify the detailed mechanism and the limiting potential for NRR on each catalyst. Additionally, we compared the reaction potential for NRR and hydrogen evolution reaction (HER) by calculating the adsorption free energy of H*.
In the Rux/C catalysts, ΔEAds of N* tend to become stronger and the ΔGDiss decreased, as the number of Ru atoms increased. In contrast, the reverse tendency was shown in Rux/BC catalysts between ΔGDiss and the number of Ru atoms. In the Rux/NCs, ΔGDiss for the two Ru atoms was lowest. Overall, NRR follow the dissociative mechanism on the Ru3/C, Ru1/BC, and Ru2/BC catalysts, and association mechanism on the others.
As shown in figure below, single-atomic Ru1/YCs showed obviously lower NRR potential than double- and triple-atomic Rux/YCs. In the case of Rux/C and Rux/NC, it was due to the relatively weak adsorption of N2H*. However, in Ru1/BC, the ΔEAds of N2H* was so strong that the reaction potential was relatively higher than Ru2/BC and Ru3/BC due to the strong B-N bonding. It was found that the ΔEAds of N2H* can be used as an indicator to predict NRR potential on Rux/YCs.
We compared the reaction potential for NRR and HER on each catalysts. In Ru2/NC catalyst, HER potential was lower than NRR potential, and it was found that Ru2/NC with good activity and selectivity is the most promising candidate for NRR catalyst.

Figure 1