Borate Anion Dopant Inducing Oxygen Vacancies over Co3O4 Nanocages for Enhanced Oxygen Evolution

Anode Alchemy on Multiscale: Engineering from Intrinsic Activity to Impedance Optimization for Efficient Water Electrolysis

The past decade has seen significant progress in proton exchange membrane water electrolyzers (PEMWE), but the growing demand for cost-effective electrolytic hydrogen pushes for higher efficiency at lower costs. As a complex system, the performance of PEMWE is governed by a combination of multiscale factors. This review summarizes the latest progress from quantum to macroscopic scales. At the quantum level, electron spin configurations can be optimized to enhance catalytic activity. At the nano and meso scales, advancements in atomic structure optimization, crystal phase engineering, and heterostructure design improve catalytic performance and mass transport. At the macro scale, innovative techniques in gas bubble management and internal resistance reduction drive further efficiency gains under ampere-level operating conditions. These modifications at the quantum level cascade through meso- and macro-scales, affecting charge transfer, reaction kinetics, and gas evolution management. Unlike conventional approaches that focus solely on one scale-either at the catalyst level (e.g., atomic, or crystal modifications) or at the device level (e.g., porous transport layers design)-combining multiscale optimizations unlocks greater performance improvements. Finally, a perspective on future opportunities for multiscale engineering in PEMWE anode design toward commercial viability is offered.

Recent Progress on the Synthesis and Modified Strategies of Zeolitic-Imidazole Framework-67 Towards Electrocatalytic Oxygen Evolution Reaction

As a class of metal-organic framework, the zeolitic-imidazole framework-67 is constructed from bridging cobalt ions and 2-methylimidazole. The high content of abundant active cobalt species, uniform structure, ultrahigh porosity, and large surface area show the potential for multiple catalytic applications, especially electrocatalytic oxygen evolution reaction (OER). The design and synthetic strategies of catalyst-based ZIF-67 that approach the maximized catalytic performance are still challenging in further development. Herein, the current progress strategy on the structural design, synthetic route, and functionalization of electrocatalysts based on ZIF-67 to boost the catalytic performance of OER is reviewed. Besides, the structurally designed catalyst from various fabricated strategies corresponding to enhancing catalytic activity is discussed. The emphasized review for understanding design and synthetic structure with catalytic performance could guide researchers in further developing catalyst-based ZIF-67 for improving the efficient electrocatalytic OER.

One-pot synthesis of boron-doped cobalt oxide nanorod coupled with reduced graphene oxide for sodium ion batteries

Heteroatom doping is one of the feasible strategies to improve electrode efficiency. Meanwhile, graphene helps to optimize structure and improve conductivity of the electrode. Here, we synthesized a composite of boron-doped cobalt oxide nanorods coupled with reduced graphene oxide by a one-step hydrothermal method and investigated its electrochemical performance for sodium ion storage. Because of the activated boron and conductive graphene, the assembled sodium-ion battery shows excellent cycling stability with a high initial reversible capacity of 424.8 mAh g^-1, which is maintained as high as 444.2 mAh g^-1 after 50 cycles at a current density of 100 mA g^-1. The electrodes also exhibit excellent rate performance with 270.5 mAh g^-1 at 2000 mA g^-1, and retain 96% of the reversible capacity upon recovery from 100 mA g^-1. This study shows that boron doping can increase the capacity of cobalt oxides and graphene can stabilize structure and improve conductivity of the active electrode material, which are essential for achieving satisfactory electrochemical performance. Therefore, the doping of boron and introduction of graphene may be one of the promising means to optimize the electrochemical performance of anode materials.

Recent developments of Co3O4-based materials as catalysts for the oxygen evolution reaction

The demand for the development of clean and efficient energy is becoming increasingly pressing due to depleting fossil fuels and environmental concerns.

Photocatalytic and Electrocatalytic Properties of Cu-Loaded ZIF-67-Derivatized Bean Sprout-Like Co-TiO2/Ti Nanostructures

ZIF-derivatized catalysts have shown high potential in catalysis. Herein, bean sprout-like Co-TiO2/Ti nanostructures were first synthesized by thermal treatment at 800 °C under Ar-flow conditions using sacrificial ZIF-67 templated on Ti sheets. It was observed that ZIF-67 on Ti sheets started to thermally decompose at around 350 °C and was converted to the cubic phase Co3O4. The head of the bean sprout structure was observed to be Co3O4, while the stem showed a crystal structure of rutile TiO2 grown from the metallic Ti support. Cu sputter-deposited Co-TiO2/Ti nanostructures were also prepared for photocatalytic and electrocatalytic CO2 reduction performances, as well as electrochemical oxygen reaction (OER). Gas chromatography results after photocatalytic CO2 reduction showed that CH3OH, CO and CH4 were produced as major products with the highest MeOH selectivity of 64% and minor C2 compounds of C2H2, C2H4 and C2H6. For electrocatalytic CO2 reduction, CO, CH4 and C2H4 were meaningfully detected, but H2 was dominantly produced. The amounts were observed to be dependent on the Cu deposition amount. Electrochemical OER performances in 0.1 M KOH electrolyte exhibited onset overpotentials of 330-430 mV (vs. RHE) and Tafel slopes of 117-134 mV/dec that were dependent on Cu-loading thickness. The present unique results provide useful information for synthesis of bean sprout-like Co-TiO2/Ti hybrid nanostructures and their applications to CO2 reduction and electrochemical water splitting in energy and environmental fields.

Surface Modification of Electrocatalyst for Optimal Adsorption of Reactants in Oxygen Evolution Reaction

Technological development after the industrial revolution has improved the quality of human life, but global energy consumption continues to increase due to population growth and the development of fossil fuels. Therefore, numerous studies have been conducted to develop sustainable long-term and renewable alternative energy sources. The anodic electrode, which is one of the two-electrode system components, is an essential element for effective energy production. In general, precious metal-based electrocatalysts show high OER reactions from the anodic electrode, but it is difficult to scale up due to their low abundance and high cost. To overcome these problems, transition metal-based anodic electrodes, which exhibit advantages with respect to their low cost and high catalytic activities, are in the spotlight nowadays. Among them, stainless steel is a material with a high ratio of transition metal components, i.e., Fe, Ni, and Cr, and has excellent corrosion resistance and low cost. However, stainless steel shows low electrochemical performance due to its slow sluggish kinetics and lack of active sites. In this study, we fabricated surface modified electrodes by two methods: (i) anodization and (ii) hydrogen peroxide (H2O2) immersion treatments. As a result of comparing the two methods, the change of the electrode surface and the electrochemical properties were not confirmed in the H2O2 immersion method. On the other hand, the porous electrode (PE) fabricated through electrochemical anodization shows a low charge transfer resistance (Rct) and high OER activity due to its large surface area compared to the conventional electrode (CE). These results confirm that the synthesis process of H2O2 immersion is an unsuitable method for surface modification. In contrast, the PE fabricated by anodization can increase the OER activity by providing high adsorption of reactants through surface modification.