Yun Tong

Metallic Nickel Nitride Nanosheets Realizing Enhanced Electrochemical Water Oxidation

Exploring efficient and inexpensive oxygen evolution reaction (OER) electrocatalysts is of great importance for various electrochemical energy storage and conversion technologies. Ni-based electrocatalysts have been actively pursued because of their promising activity and earth abundance. However, the OER efficiency for most of the developed Ni-based electrocatalysts has been intrinsically limited due to their low electrical conductivity and poor active site exposure yield. Herein, we report metallic Ni3N nanosheets as an efficient OER electrocatalyst for the first time. The first-principles calculations and electrical transport property measurements unravel that the Ni3N is intrinsically metallic, and the carrier concentration can be remarkably improved with dimensional confinement. The EXAFS spectra provide solid evidence that the Ni3N nanosheets have disordered structure resultant of dimensional reduction, which then could provide more active sites for OER. Benefiting from enhanced electrical conductivity with metallic behavior and atomically disordered structure, the Ni3N nanosheets realize intrinsically improved OER activity compared with bulk Ni3N and NiO nanosheets. Our finding suggests that metallic nitride nanosheets could serve as a new group of OER electrocatalysts with excellent property.

Metallic Co4N Porous Nanowire Arrays Activated by Surface Oxidation as Electrocatalysts for the Oxygen Evolution Reaction

Designing highly efficient electrocatalysts for oxygen evolution reaction (OER) plays a key role in the development of various renewable energy storage and conversion devices. In this work, we developed metallic Co4N porous nanowire arrays directly grown on flexible substrates as highly active OER electrocatalysts for the first time. Benefiting from the collaborative advantages of metallic character, 1D porous nanowire arrays, and unique 3D electrode configuration, surface oxidation activated Co4N porous nanowire arrays/carbon cloth achieved an extremely small overpotential of 257 mV at a current density of 10 mA cm(-2), and a low Tafel slope of 44 mV dec(-1) in an alkaline medium, which is the best OER performance among reported Co-based electrocatalysts to date. Moreover, in-depth mechanistic investigations demonstrate the active phases are the metallic Co4N core inside with a thin cobalt oxides/hydroxides shell during the OER process. Our finding introduces a new concept to explore the design of high-efficiency OER electrocatalysts.

Atomically Dispersed Iron–Nitrogen Species as Electrocatalysts for Bifunctional Oxygen Evolution and Reduction Reactions

Rational design of non-noble materials as highly efficient, economical, and durable bifunctional catalysts for oxygen evolution and reduction reactions (OER/ORR) is currently a critical obstacle for rechargeable metal-air batteries. A new route involving S was developed to achieve atomic dispersion of Fe-Nx species on N and S co-decorated hierarchical carbon layers, resulting in single-atom bifunctional OER/ORR catalysts for the first time. The abundant atomically dispersed Fe-Nx species are highly catalytically active, the hierarchical structure offers more opportunities for active sites, and the electrical conductivity is greatly improved. The obtained electrocatalyst exhibits higher limiting current density and a more positive half-wave potential for ORR, as well as a lower overpotential for OER under alkaline conditions. Moreover, a rechargeable Zn-air battery device comprising this hybrid catalyst shows superior performance compared to Pt/C catalyst. This work will open a new avenue to design advanced bifunctional catalysts for reversible energy storage and conversion devices.

Strong-Coupled Cobalt Borate Nanosheets/Graphene Hybrid as Electrocatalyst for Water Oxidation Under Both Alkaline and Neutral Conditions.

Developing highly active catalysts for the oxygen evolution reaction (OER) is of paramount importance for designing various renewable energy storage and conversion devices. Herein, we report the synthesis of a category of Co-Pi analogue, namely cobalt-based borate (Co-Bi ) ultrathin nanosheets/graphene hybrid by a room-temperature synthesis approach. Benefiting from the high surface active sites exposure yield, enhanced electron transfer capacity, and strong synergetic coupled effect, this Co-Bi NS/G hybrid shows high catalytic activity with current density of 10 mA cm(-2) at overpotential of 290 mV and Tafel slope of 53 mV dec(-1) in alkaline medium. Moreover, Co-Bi NS/G electrocatalysts also exhibit promising performance under neutral conditions, with a low onset potential of 235 mV and high current density of 14.4 mA cm(-2) at 1.8 V, which is the best OER performance among well-developed Co-based OER electrocatalysts to date. Our finding paves a way to develop highly active OER electrocatalysts.

Phase-Transformation Engineering in Cobalt Diselenide Realizing Enhanced Catalytic Activity for Hydrogen Evolution in an Alkaline Medium.

Phase-transformation engineering is successfully applied in designing an alkaline hydrogen evolution reaction (HER) electrocatalyst. Benefiting from phase-transformation engineering, which endows higher electrical conductivity, ideal water adsorption energy, and faster transformation efficiency of Hads into hydrogen, cubic-phase CoSe2 realizes an enhanced electrocatalytic activity for HER under alkaline conditions.

3D Nitrogen-Anion-Decorated Nickel Sulfides for Highly Efficient Overall Water Splitting

Developing non-noble-metal electrocatalysts with high activity and low cost for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of paramount importance for improving the generation of H2 fuel by electrocatalytic water-splitting. This study puts forward a new N-anion-decorated Ni3 S2 material synthesized by a simple one-step calcination route, acting as a superior bifunctional electrocatalyst for the OER/HER for the first time. The introduction of N anions significantly modifies the morphology and electronic structure of Ni3 S2 , bringing high surface active sites exposure, enhanced electrical conductivity, optimal HER Gibbs free-energy (ΔGH* ), and water adsorption energy change (ΔGH2O* ). Remarkably, the obtained N-Ni3 S2 /NF 3D electrode exhibits extremely low overpotentials of 330 and 110 mV to reach a current density of 100 and 10 mA cm-2 for the OER and HER in 1.0 m KOH, respectively. Moreover, an overall water-splitting device comprising this electrode delivers a current density of 10 mA cm-2 at a very low cell voltage of 1.48 V. Our finding introduces a new way to design advanced bifunctional catalysts for water splitting.

Engineering the Electronic State of a Perovskite Electrocatalyst for Synergistically Enhanced Oxygen Evolution Reaction

A surface hydrogen effect to modulate the pure electronic-state transition in perovskite Ca0.9 Yb0.1 MnO3 synergistically generates a more suitable eg electron filling status and better conductivity. This achieves 100 times higher catalytic activity compared to that of a pristine sample.

A Bifunctional Hybrid Electrocatalyst for Oxygen Reduction and Evolution: Cobalt Oxide Nanoparticles Strongly Coupled to B,N‐Decorated Graphene

The electrocatalyzed oxygen reduction and evolution reactions (ORR and OER, respectively) are the core components of many energy conversion systems, including water splitting, fuel cells, and metal-air batteries. Rational design of highly efficient non-noble materials as bifunctional ORR/OER electrocatalysts is of great importance for large-scale practical applications. A new strongly coupled hybrid material is presented, which comprises CoOx nanoparticles rich in oxygen vacancies grown on B,N-decorated graphene (CoOx NPs/BNG) and operates as an efficient bifunctional OER/ORR electrocatalyst. Advanced spectroscopic techniques were used to confirm formation of abundant oxygen vacancies and strong Co-N-C bridging bonds within the CoOx NPs/BNG hybrid. Surprisingly, the CoOx NPs/BNG hybrid electrocatalyst is highly efficient for the OER with a low overpotential and Tafel slope, and is active in the ORR with a positive half-wave potential and high limiting current density in alkaline medium.

Cobalt nitrides as a class of metallic electrocatalysts for the oxygen evolution reaction

The development of highly-efficient, stable and cost-effective electrocatalysts for the oxygen evolution reaction (OER) is critical for a range of renewable-energy technologies, including metal–air batteries, fuel cells and water-splitting reactions. However, most of the well-developed electrocatalysts are semiconductors or insulators with poor conductivity, which has profoundly inhibited their overall OER efficiency. In this study, metallic cobalt nitrides (Co2N, Co3N and Co4N) arising from electron delocalization modulation have been investigated for OER electrocatalysts in alkaline solution for the first time. Benefiting from the synergistical engineering of the electrical conductivity and nitrogen content, the simple metallic Co4N catalyst without modifications exhibits a stable current density of 10 mA cm−2 at a small overpotential of 330 mV for OER with a Tafel slope as low as 58 mV dec−1 in alkaline medium, which is superior to most of the unmodified metal oxide electrocatalysts reported to date. Our finding introduces new possibilities for the design of highly active electrocatalysts using synergistical electrical conductivity regulation and composition modulation.

Half-Metallic Behavior in 2D Transition Metal Dichalcogenides Nanosheets by Dual-Native-Defects Engineering

Two-dimensional transition metal dichalcogenides (TMDs) have been regarded as one of the best nonartificial low-dimensional building blocks for developing spintronic nanodevices. However, the lack of spin polarization in the vicinity of the Fermi surface and local magnetic moment in pristine TMDs has greatly hampered the exploitation of magnetotransport properties. Herein, a half-metallic structure of TMDs is successfully developed by a simple chemical defect-engineering strategy. Dual native defects decorate titanium diselenides with the coexistence of metal-Ti-atom incorporation and Se-anion defects, resulting in a high-spin-polarized current and local magnetic moment of 2D Ti-based TMDs toward half-metallic room-temperature ferromagnetism character. Arising from spin-polarization transport, the as-obtained T-TiSe1.8 nanosheets exhibit a large negative magnetoresistance phenomenon with a value of -40% (5T, 10 K), representing one of the highest negative magnetoresistance effects among TMDs. It is anticipated that this dual regulation strategy will be a powerful tool for optimizing the intrinsic physical properties of TMD systems.