Unravelling the factors that control the activity and stability of catalysts for alkaline water electrolysis

绿色氢是我们向净零未来过渡的重要能源载体。今天生产的几乎所有绿色氢都来自碱性电解水。以nixyyhz为基料的稀土富集催化剂作为阴极析氢反应的催化剂。虽然碱性电解槽是一项成熟的技术，但人们对工业电解槽中使用的nixyhz催化剂的活性和稳定性的来源知之甚少1,2。据报道，对于阴极析氢反应，在前40小时的操作中，过电位增加了约0.35 V。这种下降可以通过在晶格中加入铁来防止。然而，目前尚不清楚活性催化相是氧化物、金属还是氢化物。此外，触发和/或放大失活的循环和稳态条件是未知的。获得这些见解将使我们能够确定非贵金属基催化剂析氢活性和稳定性的极限，并设计出比目前最先进的催化剂更好的催化剂。在这个项目中，学生将合成NixOyHz和掺铁NixOyHz催化剂，并在一系列不同的操作方案下进行电化学活性和稳定性测试。样品将使用x射线吸收和x射线光发射光谱来确定金属中心和表面中间体的氧化状态（作为电位的函数），以及中子衍射和原子探针层析成像来确定形貌，特别是（氧）氢氧化物或氢化物相的存在。

Green hydrogen is an important energy vector in our transition to a net-zero future. Almost all green hydrogen produced today is from alkaline water electrolysis. Earth-abundant catalysts based on NixOyHz are used as catalysts for the cathodic hydrogen evolution reaction. Although alkaline electrolysers are a mature technology, very little is known about the origin of the activity and stability of NixOyHz catalysts used in industrial electrolysers1,2. It has been reported that for the cathodic hydrogen evolution reaction, the overpotential increases by approximately 0.35 V during the first 40 hours of operation. This drop can be prevented by incorporating Fe into the lattice3. However, it is not clear whether the active catalytic phase is an oxide, a metal or a hydride1. Moreover, the cycling and steady state conditions that trigger and/or amplify the deactivation is unknown. Gaining such insights would allow us to determine the limits to activity and stability of non-precious metal-based catalysts for hydrogen evolution and to design better catalysts that outperform the current state-of-the-art. In this project, the student will synthesise NixOyHz and Fe-doped NixOyHz catalysts and perform electrochemical activity and stability tests for a range of different operation protocols. The samples will be characterised using X-ray absorption and X-ray photoemission spectroscopy to determine the oxidation state of the metal centre and surface intermediates as a function of potential as well as neutron diffraction and atom probe tomography to determine the morphologies, particularly the presence of (oxy)hydroxide or hydride phases.