Designing nanostructured materials with modified surface structures, which exhibit interesting properties and applications, is of great importance. The ability to modify the physical and chemical properties of hafnium oxide not only alters the optical properties but also makes it a suitable candidate for electrocatalytic systems. In this work, we report a simple, cost-effective method to fabricate oxygen-vacancy-enriched HfO_2–x supported reduced graphene oxide (HfO_2–x/rGO) using the microwave-assisted method and investigate their optical and electrocatalytic properties. The synthesized HfO_2–x/rGO with particle size down to ∼2.2 nm exhibits a characteristic photoluminescence peak at 434 nm (2.85 eV) indicative of surface defects related to oxygen vacancies as corroborated by electron-spin resonance and X-ray photoelectron spectroscopy that reveals ∼61% of HfO_2–x are in the reduced state of Hf³⁺. Owing to its high surface defects related to oxygen vacancies and improved conductivity, its electrocatalytic applications toward hydrogen evolution reaction in acidic media exhibited a low overpotential of −0.32 V_RHE at 10 mA cm^–2 compared to their bulk and fully oxidized counterparts. This simple experimental strategy for designing highly surface defect-rich transition metal oxides to make them electrocatalytically active for energy applications is indeed interesting.

中文翻译：

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还原氧化石墨烯负载的富氧空位 HfO2–x 纳米颗粒用于电催化析氢反应

设计具有改性表面结构的纳米结构材料，使其表现出有趣的特性和应用，非常重要。改变氧化铪物理和化学性质的能力不仅改变了光学性质，而且使其成为电催化系统的合适候选者。在这项工作中，我们报告了一种简单、经济有效的方法，利用微波辅助方法制备富氧空位的 HfO _{2– x}负载的还原氧化石墨烯（HfO _{2– x /rGO），并研究其光学和电催化性能。}合成的 HfO _{2 – x} /rGO 粒径小至 ∼2.2 nm，在 434 nm (2.85 eV) 处表现出特征光致发光峰，表明与氧空位相关的表面缺陷，经电子自旋共振和 X 射线光电子能谱证实，揭示~61%的HfO _{2– x}处于Hf ³⁺的还原态。由于其与氧空位相关的高表面缺陷和改进的电导率，其在酸性介质中析氢反应的电催化应用中，与本体和完全氧化的对应物相比，在 10 mA cm ^{–2下表现出 -0.32 V} _RHE的低过电势。这种简单的实验策略用于设计高度表面缺陷丰富的过渡金属氧化物，使其在能源应用中具有电催化活性，确实很有趣。