Nitrogen Engineering on 3D Dandelion‐Flower‐Like CoS₂ for High‐Performance Overall Water Splitting

Abstract

Searching for highly efficient and stable bifunctional electrocatalysts toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is highly desirable for the practical application of water electrolysis under alkaline electrolyte. Although electrocatalysts based on transition metal sulfides (TMSs) are widely studied as efficient (pre)catalysts toward OER under alkaline media, their HER performances are far less than the state‐of‐the‐art Pt catalyst. Herein, the synthesis of nitrogen doped 3D dandelion‐flower‐like CoS2 architecture directly grown on Ni foam (N‐CoS2/NF) is reported that possesses outstanding HER activity and durability, with an overpotential of 28 mV to obtain the current density of 10 mA cm−2, exceeding almost all the documented TMS‐based electrocatalysts. Density functional theory calculations and experimental results reveal that the d‐band center of CoS2 could be efficiently tailored by N doping, resulting in optimized adsorption free energies of hydrogen (ΔG*H) and water , which can accelerate the HER process in alkaline electrolyte. Besides, the resulting N‐CoS2/NF also displays excellent performance for OER, making it a high‐performance bifunctional electrocatalyst toward overall water splitting, with a cell voltage of 1.50 V to achieve 10 mA cm−2.

Cation‐Modulated HER and OER Activities of Hierarchical VOOH Hollow Architectures for High‐Efficiency and Stable Overall Water Splitting

“…Second, partially overlapped of layered areas can be distinguished as marked with two different dashed lines in color, according to the different contrast and lattice direction. Third, numerous lattice defects with the diameter of ≈5 nm (marked by red circle) are disclosed, meaning more active sites exposure, which would be beneficial for the enhanced catalytic performance . Besides, the ring‐like mode in the selected area electron diffraction (SAED) pattern also confirms the presence of polycrystalline orthorhombic γ‐FeOOH, matching well with the results of powder XRD (Figure a).…”

Nitrogen‐Doped Cobalt Pyrite Yolk–Shell Hollow Spheres for Long‐Life Rechargeable Zn–Air Batteries

“…[10][11][12][13][14] Among these electrocatalysts, transition metal sulfides, in particular cobalt sulfides, including Co 9 S 8 , CoS, Co 3 S 4 , and CoS 2 , have been widely studied as efficient precatalysts toward OER under alkaline conditions and catalysts for ORR in acidic/alkaline electrolytes. [15][16][17][18] Their good electronic conductivity, versatile redox properties, as well as unsaturated transition metal sites are favorable for adsorbing OH − and oxygen-containing intermediates on the surface. In particular, metallic cobalt pyrite (CoS 2 ) shows high intrinsic conductivity for fast charge transfer, which makes it uniquely advantageous as an OER precatalyst.…”

“…[27,28] Moreover, compared with N-doped carbon, Ndoped transition metal-based materials are expected to be more efficient for OER/ORR to overcome the intrinsic activation barriers and facilitate reaction kinetics due to their d-band centers closer to the Fermi levels. [15,29,30] With these considerations in mind, we have developed an effective strategy to engineer CoS 2 with a porous yolk-shell structure and nitrogen doping through a facile hydrothermal and subsequent low-temperature vulcanization approach. Different from the usage of highly corrosive NH 3 gas as the common nitrogen source, ammonium hydroxide is used here as both the etchant and nitrogen source, which ensures that the yolk-shell structure of the catalyst remains intact during the post-annealing process.…”

Coupling NiCo Alloy and CeO2 to Enhance Electrocatalytic Hydrogen Evolution in Alkaline Solution

“…The performance for the NiCo-CeO 2 ||NiCo(OH) x -CeO 2 electrolyzer also outperforms most recently reported electrolyzers based on non-noble bifunctional electrocatalysts (Figure 5e; Table S4, Supporting Information). [45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] The excellent overall water splitting activity of the NiCo-CeO 2 ||NiCo(OH) x -CeO 2 electrolyzer is not only attributed to the high intrinsic catalytic activities of NiCo-CeO 2 / GP and NiCo(OH) x -CeO 2 /GP, but also to the self-supported electrode structure. Due to the in situ growth of active species on conductive substrate, the interface resistances of the self-supported NiCo-CeO 2 /GP and NiCo(OH) x -CeO 2 /GP electrodes are greatly lower than those of the Pt/C(20%)/GP and RuO 2 /GP electrodes by physically coating (Figure S25, Supporting Information), which are conducive to the rapid electron transfer.…”