A stable and cost effective oxygen evolution reaction (OER) catalyst is crucial for the large-scale market penetration of proton exchange membrane (PEM) water electrolyzers. We show that the synthesis of iridium nanoparticles in either low purity ethanol or water, or in the absence of a surfactant, is detrimental to the electrocatalytic properties of the materials. Adding NaBH₄ in excess improves the purity of the catalyst enhancing the OER activity up to 100 A g_Ir⁻¹ at 1.51 V vs. RHE, the highest value reported so far for high purity Ir nanoparticles. The measured OER activity correlates with the capacitive current rather than with the charge corresponding to the Ir^III/Ir^IV oxidation peak. Operando near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) on membrane electrode assemblies (MEAs) with the synthesized catalysts reveals a metallic core surrounded by a thin layer of Ir^III/IV oxides/hydroxides. Oxidation of Ir^III leaves behind a porous ultrathin layer of Ir^IV oxides/hydroxides, which dominate the surface during the OER, while Ir^V was not detected.

中文翻译：

---

高活性纳米铱催化剂：质子交换膜电解槽中的合成和操作光谱†

稳定且具有成本效益的析氧反应（OER）催化剂对于质子交换膜（PEM）水电解槽的大规模市场渗透至关重要。我们表明，在低纯度乙醇或水中，或者在没有表面活性剂的情况下合成铱纳米粒子，都不利于材料的电催化性能。添加过量的NaBH ₄提高了催化剂的纯度，从而在1.51 V vs. RHE下将OER活性提高至100 A g _Ir ^-1，这是迄今为止报道的高纯度Ir纳米颗粒的最高值。^{测量的 OER 活性与电容电流相关，而不是与 Ir III} /Ir ^IV氧化峰对应的电荷相关。使用合成催化剂对膜电极组件 (MEA) 进行近环境压力 X 射线光电子能谱 (NAP-XPS) 显示金属核被一层薄层 Ir ^III/IV氧化物/氢氧化物包围。Ir ^{III的氧化留下了 Ir IV}氧化物/氢氧化物的多孔超薄层，其在 OER 过程中占据了表面，而 Ir ^V则没有被检测到。