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 NiCo₂S₄ nanoflakes grown on nickel foam (NiCo₂S₄/Ni foam) can serve as excellent electrocatalyst for HER in alkaline solution with high activity and stability. The NiCo₂S₄/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 NiCo₂S₄ 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 NiCo₂S₄/Ni foam electrodes exhibit greatly improved performance than NiCo-LDH/Ni foam for HER in alkaline solution with low onset overpotential (17mV), small Tafel slope (84.5mV/dec) and excellent long-duration cycling stability (maintaining an onset overpotential of ~20mV and an overpotential of 155mV at 50mA/cm² after testing for 100,000seconds). In addition, the highly-flexible NiCo₂S₄/Ni foam electrodes show no obvious catalytic degradation after bending for 200 times, confirming the high flexibility and robustness under severe conditions.

中文翻译：

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在镍泡沫上生长的自组装超薄NiCo2S4纳米薄片，作为高性能的柔性电极，可在碱性溶液中发生氢气分解反应

在高性能和低成本的用于氢气析出反应（HER）的非铂电催化剂的设计和制造方面已经进行了相当大的努力。然而，现有电催化剂的催化活性通常受到有限量的暴露的活性位点的影响。在此，我们提出在镍泡沫上生长的自组装超薄NiCo ₂ S ₄纳米薄片（NiCo ₂ S ₄ / Ni泡沫）可以作为碱性溶液中HER的优良电催化剂，具有高活性和稳定性。NiCo ₂ S ₄/ Ni泡沫电极是通过完全硫化在Ni泡沫（NiCo-LDH / Ni泡沫）上生长的网络化超薄NiCo层状双氢氧化物纳米薄片而制备的。这种独特的体系结构的优势在于：超薄且多孔的NiCo ₂ S ₄纳米薄片可以提供大量的暴露活性位点；高导电性的Ni泡沫可以促进电子的转移；三维网络结构可以促进电解质的扩散和渗透。电化学测量表明，NiCo ₂ S ₄/ Ni泡沫电极在碱性溶液中比HER的NiCo-LDH / Ni泡沫具有显着改善的性能，具有较低的起始过电势（17mV），小的Tafel斜率（84.5mV / dec）和出色的长期循环稳定性（保持起始过电势为测试100,000秒后，在50mA / cm ^2时约为20mV和155mV的过电势）。此外，高柔韧性的NiCo ₂ S ₄ / Ni泡沫电极弯曲200次后没有明显的催化降解，证实了在严苛条件下的高柔韧性和坚固性。