利用可再生能源发电,并通过低温电解水技术生产氢气,被认为是一种环保且可持续的制氢途径,是未来氢能发展的重要方向之一.采用该方法生产的氢气因其环保特性而被称为"绿氢".然而,目前绿氢高昂的生产成本限制了电解水制氢技术的大规模应用.因此,开发先进的非贵金属催化剂和电催化体系以降低电解水制氢成本具有重要意义.界面工程是一种提升非贵金属催化剂电解水性能的有效策略,但目前对其催化活性位点的识别及活性提升机制的研究仍然不足.本文采用简单的水热及低温磷化法制备了具有丰富异质界面的Ni2P/CoP/FeP4/IF催化剂,并研究了其在电解水过程中的催化活性位点及这些位点在提升催化能力方面的协同作用.采用扫描电镜(SEM)证明了Ni2P/CoP/FeP4/IF催化剂呈现纳米线网络结构,这种结构不仅有利于增加催化剂的电化学活性位点和加速反应动力学,而且促进了连续产生的气泡从活性位点逃逸,从而提高了催化剂的机械稳定性.电化学研究结果表明,所制备Ni2P/CoP/FeP4/IF催化剂在1.0 mol L-1 KOH溶液中表现出较好的析氧反应(OER)和析氢反应(HER)活性,分别仅需218和127 mV的过电位,即可达到100 mA cm-2的电流密度.将Ni2P/CoP/FeP4/IF分别作为阴极和阳极构建双电极电解槽,该装置产生100和500 mA cm-2的电流密度分别仅需1.68和2.05 V的电压,这一性能优于大多数已报道的自支撑过渡金属磷化物催化剂.多步计时电位测试结果进一步证实了Ni2P/CoP/FeP4/IF作为阳极和阴极材料在水分解过程中具有较好的长期耐久性.X射线光电子能谱和差分电荷分析表明,电子从富电子的FeP4向缺电子的Ni2P和CoP转移,这促使Ni2P和CoP上的电子积累和FeP4上的空穴积累,有利于优化反应中间体的吸附和脱附自由能,提升OER和HER催化性能.结合X射线衍射、扫描电镜、透射电镜、X射线光电子能谱和原位拉曼光谱结果发现,催化剂重构后形成的特定(氧)氢氧化物结构,是OER反应真正的关键活性位点.原位拉曼光谱进一步证实了异质界面促进了OER过程中Ni2P/CoP/FeP4/IF的快速重构.此外,利用密度泛函理论分析了催化剂的HER反应机理.计算结果表明,H2O优先吸附在Fe位点并发生水解,随后产生的H*吸附在Ni位点上并发生解吸,从而促进了催化剂中Fe和Ni活性位点的高效利用.同时,CoP的引入提高了Ni2P/CoP/FeP4/IF催化剂的水吸附和解离能力,进一步提升了其HER活性.综上所述,本文通过简单的水热及低温磷化法制备了具有丰富异质界面的Ni2P/CoP/FeP4/IF过渡金属磷化物纳米线网络催化剂,并将其用于碱性水分解.通过多种表征技术及理论计算结果分析,识别了电解水过程中的关键催化活性位点,即催化剂重构后形成的特定(氧)氢氧化物结构,并揭示了其在OER和HER反应中的催化机制.本研究可为高性能碱性电解水催化剂的理性设计和开发提供参考.
In situ surface reconstruction of heterostructure Ni2P/CoP/FeP4 nanowires network catalyst for high-current-density overall water splitting
Considering the imperative need for cost-effective electrocatalysts for water electrolysis,a novel Ni2P/CoP/FeP4/IF electrocatalyst nanowires network was synthesized in this study.Owing to the strong synergistic effects and high exposure of the active sites,Ni2P/CoP/FeP4/IF exhibited excep-tional performance in both the oxygen evolution reaction(OER)and hydrogen evolution reaction(HER),demonstrating low overpotentials of 218 and 127 mV at 100 mA cm-2 in alkaline media,respectively.Furthermore,the water electrolyzer based on Ni2P/CoP/FeP4/IF bifunctional catalyst requires only 1.50 and 2.05 V to reach 10 and 500 mA cm-2,respectively,indicating its potential for large-scale hydrogen production.Comprehensive ex situ characterizations and in situ Raman spec-tra reveal that Ni2P/CoP/FeP4/IF undergoes rapid reconstruction during the OER to form the cor-responding(oxy)hydroxide species,which serve as the real active sites.Furthermore,density func-tional theory calculations clarified that during the HER process,H2O is adsorbed at the Fe site of Ni2P/CoP/FeP4/IF for hydrolysis,with the resultant H*adsorbed at the Ni site for desorption.In-troducing CoP promoted water adsorption and increased the HER activity of the catalyst.Hence,this study offers a pathway for designing highly efficient catalysts that leverage the interface effects.
Overall water splittingMulti-interfacesPhosphideSurface reconstructionHigh-current-density
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