Enhanced Water Oxidation Activity of the Cobalt(II,III) Oxide Electrocatalyst on an Earth-Abundant-Metal-Interlayered Hybrid Porous Carbon Support

Isovalent anion-induced electrochemical activity of doped Co3V2O8 for oxygen evolution reaction application

The activity of an OER electrocatalyst is a strong function of the reaction kinetics at the active sites, which can be influenced by catalytic engineering (e.g., heterostructure, doping, and the addition of cocatalysts). Herein, we report the improved reaction kinetics of cobalt oxide for the OER via the addition of high valence vanadium and thereafter doping with sulphur (S-Co₃V₂O₈). The addition of vanadium increases the oxygen vacancy while the doping of sulphur increases the electronic conductivity of the electrocatalyst. The synergic effect of the oxygen vacancy and electronic conductivity increases the activity of S-Co₃V₂O₈. Furthermore, S-Co₃V₂O₈ showed the least Tafel slope, which showed the activity enhancement towards the oxygen evolution reaction. Moreover, the underlying reaction mechanism is explored by electrochemical impedance spectroscopy, which reveals that the ratio of polarisation resistance to double-layer capacitance is minimum for S-Co₃V₂O₈, indicating the highest activity.

Engineering Amorphous/Crystalline Structure of Manganese Oxide for Superior Oxygen Catalytic Performance in Rechargeable Zinc-Air Batteries

Although amorphous materials are popular in oxygen electrocatalysis, their performance requires further improvement to meet the need for rechargeable zinc-air batteries. In this work, an amorphous/crystalline layered manganese oxide (ACMO) was designed, and its unique amorphous/crystalline homogeneous structure activated its oxygen reduction activity with a positive half-wave potential of 0.81 V and oxygen evolution activity with a moderate overpotential of 407 mV at 10 mA cm^-2 . Moreover, the amorphous/crystalline structure endowed ACMO with excellent stability. While employed as the air-electrode material for rechargeable zinc-air batteries, ACMO overcame the poor cycling stability of manganese oxide and cycled stably for 1000 cycles (≈17 days) at 10 mA cm^-2 . Besides, it delivered a high power density of 159.7 mW cm^-2 and a narrow voltage gap of 0.66 V. This work gives an insight into designing oxide materials with amorphous/crystalline structure and feasible guidance for harmonizing electrochemical activity and stability.

Functionality and design of Co-MOFs: unique opportunities in electrocatalysts for oxygen reduction reaction

The first report highlighting miraculous and intelligent electrocatalysts that can be tailored to form useful structures and morphologies with active sites for the oxygen reduction reaction.

High-performance AEM unitized regenerative fuel cell using Pt-pyrochlore as bifunctional oxygen electrocatalyst

The performance of fixed-gas unitized regenerative fuel cells (FG-URFCs) are limited by the bifunctional activity of the oxygen electrocatalyst. It is essential to have a good bifunctional oxygen electrocatalyst which can exhibit high activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In this regard, Pt-Pb₂Ru₂O_7-x is synthesized by depositing Pt on Pb₂Ru₂O_7-x wherein Pt individually exhibits high ORR while Pb₂Ru₂O_7-x shows high OER and moderate ORR activity. Pt-Pb₂Ru₂O_7-x exhibits higher OER (η_@10mAcm-2 = 0.25 ± 0.01 V) and ORR (η_@-3mAcm-2 = -0.31 ± 0.02 V) activity in comparison to benchmark OER (IrO₂, η_@10mAcm-2 = 0.35 ± 0.02 V) and ORR (Pt/C, η_@-3mAcm-2 = -0.33 ± 0.02 V) electrocatalysts, respectively. Pt-Pb₂Ru₂O_7-x shows a lower bifunctionality index (η_{@10mAcm-2, OER} ^- η_{@-3mAcm-2, ORR}) of 0.56 V with more symmetric OER-ORR activity profile than both Pt (>1.0 V) and Pb₂Ru₂O_7-x (0.69 V) making it more useful for the AEM (anion exchange membrane) URFC or metal-air battery applications. FG-URFC tested with Pt-Pb₂Ru₂O_7-x and Pt/C as bifunctional oxygen electrocatalyst and bifunctional hydrogen electrocatalyst, respectively, yields a mass-specific current density of 715 ± 11 A/g_cat ^-1 at 1.8 V and 56 ± 2 A/g_cat ^-1 at 0.9 V under electrolyzer mode and fuel-cell mode, respectively. The FG-URFC shows a round-trip efficiency of 75% at 0.1 A/cm^-2, underlying improvement in AEM FG-URFC electrocatalyst design.

Climbing with support: scaling the volcano relationship through support–electrocatalyst interactions in electrodeposited RuO2 for the oxygen evolution reaction

The interfacial charge transfer and support-induced electrocatalyst faceting in thin catalysts enable ‘climbing up’ the volcano map for OER electrocatalysts. The conductivity of the support determines the OER activity of thick catalysts.

In Situ Electrodeposition of Cobalt Sulfide Nanosheet Arrays on Carbon Cloth as a Highly Efficient Bifunctional Electrocatalyst for Oxygen Evolution and Reduction Reactions

As one of the advanced cobalt-based materials, cobalt sulfides with novel architecture have attracted huge interest due to the low cost, easy availability, and promising bifunctional activity for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which is essential for next-generation energy storage devices. Herein, we demonstrated a facile and clean electrochemical technique to directly synthesize CoS nanosheets with high purity onto the surface of carbon cloth, and a quick thermal treatment was performed to further improve the catalytic performance (CoS-A). This novel electrochemical technique avoids the use of the binder, surfactant, and other organic additives, which may cause poor electric conductivity as well as undesirable surface wettability, exhibiting great potential of the large-scale applications. The obtained CoS-A exhibits a superior electrocatalytic performance for the OER and ORR, with a high ORR current density (-1.51 mA cm^-2 at 0.2 V), considerable OER current density (148 mA cm^-2 at 1.9 V), and excellent durability in continuous measurement for over 12 h. The approach offers a powerful yet simple method to control the phase, composition, and morphology of a highly active CoS catalyst, which provides a new idea for the design of high-performance catalysts.

Dissolution induced self-selective Zn- and Ru-doped TiO2 structure for electrochemical generation of KClO3

We demonstrate an electrochemical approach to prepare a highly active and stable (Zn, Ru)-doped TiO₂ (Ru_0.26Ti_0.73Zn_0.01O_x) for electrochemical generation of KClO₃.

Co3O4-δ Quantum Dots As a Highly Efficient Oxygen Evolution Reaction Catalyst for Water Splitting

Co₃O_4-δ quantum dots (Co₃O_4-δ-QDs) with a crystallite size of approximately 2 nm and oxygen vacancies were fabricated through multicycle lithiation/delithiation of mesoporous Co₃O₄ nanosheets. Used as an oxygen evolution reaction (OER) electrocatalyst for water splitting, the catalytic performance (an overpotential of 270 mV@10 mA cm^-2 and no decay within 30 h) of Co₃O_4-δ-QDs is superior to that of previously reported Co-based catalysts and the state-of-the-art IrO₂. Compared to that of the Co₃O₄ nanosheets, the enhanced OER activity of Co₃O_4-δ-QDs is attributed to two factors: one is the increased quantity of the Faradaic active sites, including the total active sites (q*_Total), the most accessible active sites (q*_Outer), and their ratio (q*_Outer/q*_Total); the other is the enhanced intrinsic electroactivity per active site evaluated by the turnover frequency and the current density normalized by the most accessible active sites (j/q*_Outer) related to the OER. This multicycle lithiation/delithiation method can be applied to other transition metal oxides as well, offering a general approach to develop high-performance electrocatalysts for water splitting.