Self-assembled ultrathin NiCo2S4 nanoflakes grown on Ni foam as high-performance flexible electrodes for hydrogen evolution reaction in alkaline solution

Abstract

Considerable efforts have been devoted on the design and fabrication of non-platinum electrocatalysts with high performance and low cost for hydrogen evolution reaction (HER). However, the catalytic activity of existing electrocatalysts usually subjects to the limited amount of exposed active sites. Herein ,we propose that self-assembled ultrathin NiCo 2 S 4 nanoflakes grown on nickel foam (NiCo 2 S 4 /Ni foam) can serve as excellent electrocatalyst for HER in alkaline solution with high activity and stability. The NiCo 2 S 4 /Ni foam electrodes were prepared by the complete sulfidation of networked ultrathin NiCo-layered double hydroxide nanoflakes grown on Ni foam (NiCo-LDH/Ni foam). The advantages of this unique architecture are that the ultrathin and porous NiCo 2 S 4 nanoflakes can provide a huge number of exposed active sites, the highly-conductive Ni foam can promote the transfer of electrons, and the three-dimensional-networked structure can facilitate the diffusion and penetration of electrolyte. Electrochemical measurements reveal that NiCo 2 S 4 /Ni foam electrodes exhibit greatly improved performance than NiCo-LDH/Ni foam for HER in alkaline solution with low onset overpotential (17 mV), small Tafel slope (84.5 mV/dec) and excellent long-duration cycling stability (maintaining an onset overpotential of ~20 mV and an overpotential of 155 mV at 50 mA/cm 2 after testing for 100,000 seconds). In addition, the highly-flexible NiCo 2 S 4 /Ni foam electrodes show no obvious catalytic degradation after bending for 200 times, confirming the high flexibility and robustness under severe conditions.

Co9S8@N,P-doped porous carbon electrocatalyst using biomass-derived carbon nanodots as a precursor for overall water splitting in alkaline media

“…[15][16][17][18][19][20] Among them, transition metal suldes such as molybdic sulde, [21][22][23] nickel sulde, [24][25][26] iron sulde 27 and cobalt sulde 28,29 have attracted considerable interest due to their earth abundance and high electrocatalytic activity. However, the poor conductivities of the transition metal suldes have limited their overall electrocatalytic performance, so they are always considered for loading on conductive substrates to improve the materials' electrical conductivity.…”

Mixed Metal Sulfides for Electrochemical Energy Storage and Conversion

“…In this context, various nanostructured nickel cobalt sulfides and their hybrids with carbon materials have been assessed for electrocatalysis. [31][32][33]88,123,[230][231][232][233][234][235][236][237][238][239] As a typical thiospinel, NiCo 2 S 4 with the conventional spinel structure possesses more octahedral electrocatalytically active sites of Co(III) cations as compared to NiCo 2 O 4 , holding potentially good bifunctional catalytic activity for both ORR and OER. [230] The bifunctional electrocatalytic properties of NiCo 2 S 4 for oxygen were first evaluated by Liu et al [33] NiCo 2 S 4 nanoparticles were loaded on nitrogen and sulfur co-doped rGO nanosheets (NiCo 2 S 4 @N/S-rGO) by a one-pot solvothermal route.…”

“…Panels (e,f): Reproduced with permission. [234] Copyright 2016, Elsevier. Panels (g,h): Reproduced with permission.…”

“…[123,231,234,235] For example, Cui et al synthesized uniform ultrathin nanosheet-assembled 3D Co 0.9 Ni 0.1 S 2 nanoballs with a size of ≈50 nm by a surfactant-assisted hydrothermal process for HER in 0.5 m H 2 SO 4 solution. [123] Thanks to the high specific surface area (62.63 m 2 g −1 ) and ultrathin nanosheet subunits, the Co 0.9 Ni 0.1 S 2 nanoballs displayed lower overpotential (152 mV vs RHE) at 10 mA cm −2 , smaller Tafel slope (52 mV dec −1 ), and larger exchange current density (4.98 µA cm −2 ) than CoS 2 nanoballs (192 mV vs RHE, 92 mV dec −1 , and 2.02 µA cm −2 ).…”

“…[31,32,234] For example, Ma et al assembled ultrathin NiCo 2 S 4 nanoflakes on NF (NiCo 2 S 4 /NF) as flexible electrode for HER in alkaline solution. [234] The NiCo 2 S 4 nanoflakes were prepared through a two-step hydrothermal approach: growth of NiCo-LDH nanoflakes on NF and the following sulfidation with TAA. The SEM image (Figure 6e) illustrates that these NiCo 2 S 4 nanoflakes were highly porous and interconnected with each other.…”