NSF-DFG Echem:Elucidating Surface Structure Contribution of Facets, Steps and Kinks in Electrocatalysis of the Oxygen Evolution and Reduction Reactions

电解是利用过剩的可再生能源生产绿色氢的关键技术，而燃料电池是将储存的化学物质有效转化为电能的关键。这两种技术都需要氧电催化作为反反应，即电解中的析氧反应（OER）和燃料电池中的氧还原反应（ORR）。不幸的是，它们缓慢的动力学导致氧半电池的高过电位限制了效率，因此需要开发改进的电催化剂。该项目的总体目标是为OER创造性能更高、更耐用的非贵金属催化剂。我们的中心假设是，控制催化剂的表面终止和表面暴露可以改变表面的配位和键合环境，从而改变反应物-催化剂相互作用和电催化OER/ORR活性。因此，催化剂的合成、表面形貌和电化学性能之间的联系对催化剂的设计至关重要。提出的工作计划目标如下：(i)合成具有确定局部活性位点的电催化剂；（ii）合成具有确定形态（孔隙、面、台阶和扭结）的电催化剂；（iii）结构表征和确定所开发的电催化剂的活性。岩盐结构可以合成具有（111）或（100）表面的形状控制的NiO颗粒，从而阐明它们在氧电催化中的作用。此外，这些材料提供了理想的平台，可以系统地研究用台阶和扭结剪裁表面的效果，以及用类似离子半径的元素（例如Co， Mn, Fe）制造多金属氧化物。Richards团队将从NiO开始，通过阳离子交换，开发纳米级多面混合金属氧化物电催化剂，包括Fe， Mn和Co。此外，将基于改进的NiO（111）气凝胶方法合成一系列多金属氧化物（如镍铁氧体）。沃克小组将采用电化学沉积以及（微波辅助）水力和溶剂热方法，形成具有相似化学计量的高多孔（有序介孔）、多面混合金属氧化物。电催化剂将使用先进的操作技术，如AFM或环境x射线光电子能谱（E-XPS）进行结构表征。对操作条件下的ORR和OER的评估将通过在GDE半电池和在Harms组试验台的mea中进行测试来解决。

Electrolysis as a key technology to generate green hydrogen uses the excess of renewable energies while fuel cells are crucial for the efficient conversion of stored chemical into electrical energy. Both technologies require oxygen electrocatalysis as counter reaction, namely the oxygen evolution reaction (OER) in electrolysis and the oxygen reduction reaction (ORR) in fuel cells. Unfortunately, their sluggish kinetics cause high overpotentials of the oxygen half-cells limiting the efficiencies and thus requiring the development of improved electrocatalysts.The overarching goal of this project is to create higher performing, more durable non-precious metal catalysts for the OER. Our central hypothesis is that controlling the surface termination and facet exposure of a catalyst can alter the coordination and bonding environments at the surface thus changing the reactant-catalyst interaction and the electrocatalytic OER/ORR activity. Therefore, the connection between synthesis, surface morphology and electrochemical performance is crucial for the design of a catalyst. The proposed work program targets following goals: (i) Synthesis of electrocatalysts with defined local active sites, (ii) Synthesis of electrocatalysts with defined morphology (pores, facets, steps and kinks) and (iii) Structural characterization and determination of the activity of the developed electrocatalysts. The rock salt structure enables synthesis of shape-controlled NiO particles with (111) or (100) surfaces allowing elucidation of their role in oxygen electrocatalysis. Further, these materials offer ideal platforms to systematically study the effects of tailoring the surfaces with steps and kinks and making multi-metal oxides with elements of similar ionic radii (e.g. Co, Mn, Fe). The Richards group will develop nanoscale faceted mixed metal oxide electrocatalysts including Fe, Mn and Co by cation exchange starting from NiO. Furthermore, a series of multi-metal oxides (e.g. nickel ferrite) will be synthesized based on a modified aerogel method developed for NiO(111). The Wark group will employ electrochemical deposition as well as (microwave-assisted) hydro- and solvothermal routes to form highly porous (with ordered mesoporosity), faceted mixed metal oxides with similar stoichiometry. The electrocatalysts will be structurally characterized using e.g. advanced operando techniques like AFM or environmental X-ray photoelectron spectroscopy (E-XPS). Evaluation of the ORR and OER under operation conditions will be addressed by tests in GDE half-cells and in MEAs in test benches in the Harms group.