Cobalt phosphides are an emerging earth‐abundant alternative to platinum‐group‐metal‐based electrocatalysts for the hydrogen evolution reaction (HER). Yet, their stability is inferior to platinum and compromises the large‐scale applicability of CoP_x in water electrolyzers. In the present study, we employed flat, thin CoP_x electrodes prepared through the thermal phosphidation (PH₃) of Co₃O₄ films made by plasma‐enhanced atomic layer deposition to evaluate their stability in acidic water electrolysis by using a multi‐technique approach. The films were found to be composed of two phases: CoP in the bulk and a P‐rich surface CoP_x (P/Co>1). Their performance was evaluated in the HER and the exchange current density was determined to be j₀=−8.9 ⋅ 10⁻⁵ A/cm². The apparent activation energy of HER on CoP_x (E_a=81±15 kJ/mol) was determined for the first time. Dissolution of the material in 0.5 M H₂SO₄ was observed, regardless of the constantly applied cathodic potential, pointing towards a chemical instead of an electrochemical origin of the observed cathodic instability. The current density and HER faradaic efficiency (FE) were found to be stable during chronoamperometric treatment, as the chemical composition of the HER‐active phase remained unchanged. On the contrary, a dynamic potential change performed in a repeated way facilitated dissolution of the film, yielding its complete degradation within 5 h. There, the FE was also found to be changing. An oxidative route of CoP_x dissolution has also been proposed.

中文翻译：

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CoPx电催化剂在连续和间断酸性水电解中的稳定性

磷化氢是一种新兴的在地球上能替代氢的铂族金属基电催化剂的替代物。然而，它们的稳定性不如铂，并且损害了CoP _x在水电解槽中的大规模应用。在本研究中，我们采用通过等离子体增强原子层沉积制备的Co ₃ O ₄膜的热磷化（PH ₃）制备的扁平，薄CoP _x电极，通过多种技术评估其在酸性水电解中的稳定性方法。发现该薄膜由两个阶段组成：整体CoP和富含P的表面CoP _x（P / Co> 1）。在HER中评估它们的性能，并且将交换电流密度确定为j ₀ = -8.9⋅10 ^-5  A / cm ²。首次确定了HER在CoP _x上的表观活化能（E _a = 81±15 kJ / mol）。将该物质溶解在0.5 MH ₂ SO _4中观察到，不管持续施加阴极电位如何，都指向观察到的阴极不稳定性的化学来源而不是电化学来源。发现在计时安培法治疗期间电流密度和HER法拉第效率（FE）稳定，因为HER活性相的化学成分保持不变。相反，以重复方式进行的动态电势变化促进了膜的溶解，从而在5小时内使其完全降解。在那里，FE也被发现正在发生变化。还提出了CoP _x溶解的氧化途径。