NiCo层状双氢氧化物负载痕量Pt的催化析氢研究

NiCo-layered double hydroxides embedded with trace platinum species for boosting alkaline hydrogen evolution reaction

  • 摘要: 降低铂的用量,提升铂基催化剂在碱性环境中的析氢反应性能,是电解水工业化应用的一个关键问题。本工作是在三电极体系中,以Pt丝对电极为Pt源,采用简单易于控制的循环伏安(Cyclic voltammetry, CV)电化学沉积方法,在水热制备的镍钴层状双氢氧化物(NiCo-LDHs)上实现了高分散Pt的痕量负载。利用NiCo-LDHs促进水的解离,Pt位点推动H的结合和脱附,有效解决Pt在碱性环境中析氢反应过程动力学滞缓的问题。在1 mol·L−1 KOH溶液中,在Pt负载量为30.4 g·cm−2时,Pt‒NiCo-LDHs电极驱动10 mA·cm−2电流密度的过电位仅需要56 mV,塔菲尔斜率仅为43 mV·decade−1,摆脱了Volmer步骤的限制,展现了优异的析氢催化活性。在100 mV的过电位下,Pt‒NiCo-LDHs的质量活性比商品化Pt/C电极高5.6倍。另外,Pt‒NiCo-LDHs在100 h的恒电流测试中表现出了良好的稳定性。

     

    Abstract: Reducing the amount of platinum (Pt) and improving the efficiency of the hydrogen evolution reaction (HER) in alkaline media is a key issue for the industrial production of hydrogen. Unlike HER under acidic conditions, the hydrogen adsorbed-atom (Had) has to be discharged from the water molecule rather than from the hydronium cation (H3O+). Pt catalysts have outstanding H adsorption and desorption free energy but are not conducive to catalyze the dissociation of water, which is the main reason for their hysteresis in alkaline HER. The combination of Pt and a cocatalyst effectively cleave the O–H bonds is an effective strategy to improve the reaction kinetics in the alkaline HER. Currently, in an alkaline electrolyte, non-noble metal hydroxide catalysts are very active for oxygen evolution reaction (OER), especially the Ni–Co hydroxide (NiCoOxHy), which effectively promotes OER owing to its excellent water dissociation ability. In this work, in a three-electrode system, a Pt wire counter electrode was used as the Pt source. Cyclic voltammetry (CV) electrochemical deposition was used to load a trace amount of Pt species onto the NiCo-layered double hydroxides (NiCo-LDHs) prepared using hydrothermal reaction on a nickel foam substrate. NiCo-LDHs can promote the dissociation of water in alkaline media, and Pt sites are beneficial for the binding and desorption of H on the electrode surface. The combination of Pt and NiCo-LDHs effectively paves a new way to enhance the slow kinetics of the hydrogen evolution reaction of Pt in an alkaline medium. The hybrid catalyst Pt‒NiCo-LDHs shows considerably improved HER performance, with a small overpotential of 56 mV to drive a typical current density of 10 mA·cm−2 and a low Tafel slope of 43 mV·decade−1 in alkaline media at an ultralow Pt loading of 30.4 g·cm−2. The mass activity of Pt‒NiCo-LDHs is 5.6 times higher than that of a commercial Pt/C catalyst with a 100 mV overpotential. Moreover, the Pt‒NiCo-LDHs catalyst exhibits outstanding stability after a 100 h test.

     

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