The deployment of water electrolysis as a major contributor to global hydrogen production requires the elimination of catalysts based on scarce and expensive precious metals, and amongst the most promising alternatives are first-row transition metal phosphides. This study presents the synthesis, characterisation, electrochemical testing and performance rationalisation of cobalt phosphide modified with aluminium as an improved catalyst for alkaline oxygen evolution. The electrodes were prepared by gas phase phosphorisation of Al-sputtered Co foam, and characterised by SEM, EDX, XRD, XPS, HAADF-STEM and Raman spectroscopy. Al modification enhances the oxygen evolution performance of the anodes, with a current density of 200 mA cm⁻² reached at an overpotential of 360 mV, representing a 50 mV improvement compared to the Al-free sample. Double layer capacitance measurements indicate that the performance enhancement results from an approximately four-fold increase in relative electrochemically active surface area (ECSA) in the Al-modified sample. In situ Raman spectroscopy rationalises this ECSA increase on the grounds of an Al-induced preference for a spinel phase Co/Al oxide on the catalyst surface upon exposure to electrolyte solution, the compact crystal structure of which causes shrinkage and surface cracking. This contrasts with previous observations on Al-doped nickel phosphides, where an increase in surface area was attributed to Al dissolution. These results present a route for achieving high current density oxygen evolution without the need to alter the catalyst active species, as well as demonstrate the importance of in situ techniques for rationalising performance improvements resulting from subtle differences in surface chemistry.

中文翻译：

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铝掺杂磷化钴通过原位表面积增加而增强的氧逸出催化作用

水电解作为全球氢气生产的主要贡献者，需要消除基于稀有且昂贵的贵金属的催化剂，最有希望的替代方法是第一行过渡金属磷化物。这项研究提出了铝改性的磷化钴作为碱性氧气释放的改进催化剂的合成，表征，电化学测试和性能合理化。电极通过铝溅射的Co泡沫的气相磷化制备，并通过SEM，EDX，XRD，XPS，HAADF-STEM和拉曼光谱进行表征。Al修饰具有200 mA cm ^-2的电流密度，可增强阳极的氧气释放性能达到360 mV的过电势，与无铝样品相比提高了50 mV。双层电容测量表明，性能增强是由于Al改性样品中的相对电化学活性表面积（ECSA）大约增加了四倍。原位拉曼光谱法使这种ECSA的增加合理化，其原因是铝在暴露于电解质溶液后在催化剂表面上偏好于尖晶石相Co / Al氧化物，这是由于铝引起的，后者的致密晶体结构会导致收缩和表面开裂。这与以前对掺铝磷化镍的观察结果相反，后者的表面积增加归因于铝的溶解。这些结果提出了无需改变催化剂活性物质即可实现高电流密度氧释放的途径，并且证明了就地技术对合理化由表面化学上的细微差别引起的性能改进的重要性。