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NiCo層狀雙氫氧化物負載痕量Pt的催化析氫研究

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

  • 摘要: 降低鉑的用量,提升鉑基催化劑在堿性環境中的析氫反應性能,是電解水工業化應用的一個關鍵問題。本工作是在三電極體系中,以Pt絲對電極為Pt源,采用簡單易于控制的循環伏安(Cyclic voltammetry, CV)電化學沉積方法,在水熱制備的鎳鈷層狀雙氫氧化物(NiCo-LDHs)上實現了高分散Pt的痕量負載。利用NiCo-LDHs促進水的解離,Pt位點推動H的結合和脫附,有效解決Pt在堿性環境中析氫反應過程動力學滯緩的問題。在1 mol·L?1 KOH溶液中,在Pt負載量為30.4 g·cm?2時,Pt?NiCo-LDHs電極驅動10 mA·cm?2電流密度的過電位僅需要56 mV,塔菲爾斜率僅為43 mV·decade?1,擺脫了Volmer步驟的限制,展現了優異的析氫催化活性。在100 mV的過電位下,Pt?NiCo-LDHs的質量活性比商品化Pt/C電極高5.6倍。另外,Pt?NiCo-LDHs在100 h的恒電流測試中表現出了良好的穩定性。

     

    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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