Unusual Defective Dicubane Azide Bridge Tetranuclear NiII4‑Cluster: Highly Active and Stable Electrocatalyst for Hydrogen Evolution Reaction

Designing highly efficient, environmentally friendly, sustainable, and durable catalysts for water electrolysis is vital for advancing renewal energy systems due to the continued reliance on fossil fuels leading to energy shortages and rapid environmental pollution. In this work, we have synthesized a tetranuclear centrosymmetric, unusual azide-bridged (end-on) NiII4N4O2 defective dicubane core with all hexacoordinated nickel(II) atoms via a simple slow evaporation method. [C42H50Ni4N16O10] (Ni4-cluster) has an orthorhombic crystal system with space group Pbca, distorted octahedral of each nickel center to the formation of a tetranuclear nickel cluster. Single-crystal X-ray diffraction (SCXRD) analyses reveal that the cluster is tetranuclear with μ2-(1,1-azido) and μ3-(1,1,1-azido) bridges. The Ni4-cluster shows a highly active and stable electrocatalyst for hydrogen evolution reaction (HER) in a 0.25 M acetate buffer electrolyte (pH = 3.8), achieving a low overpotential of only 287 mV at 10 mA cm–2 current density, with high double-layer capacitance (Cdl) (0.34 mF cm–2) and low charge-transfer resistance (17.6 Ω). The intrinsic parameters such as Tafel slope (316 mV dec–1), turnover frequency (TOF) (1.82 s–1 at 350 mV), and exchange current density (0.002 A cm–2) correlate to the fair electrocatalytic activity of the Ni4-cluster cathode for the HER. The electrode remained stable for over 25 h at a constant current density of −10 mA cm–2. The Ni4-cluster delivered over 92% Faradaic efficiency for hydrogen production in the 0.25 M acetate buffer electrolyte. Compared all the electrochemical analyses, the Ni4-cluster reported that it is more active, efficient, and sustainable for H2 production and makes it an auspicious candidate in the field of energy conversion application.鉴于化石燃料的持续依赖引发能源短缺与快速加剧的环境污染，设计高效、环保、可持续且耐用的电解水催化剂，对于推动可再生能源（renewable energy）系统发展至关重要。本研究通过简易缓慢挥发法，合成了一种四核中心对称、少见的端基配位型（end-on）叠氮桥联NiII4N4O2缺陷双立方烷核结构，所有镍(II)原子均为六配位。化学式为[C42H50Ni4N16O10]的镍四核团簇（Ni4-cluster）属于正交晶系（orthorhombic crystal system），空间群为Pbca，每个镍中心呈畸变八面体配位，由此构建出四核镍团簇。单晶X射线衍射（single-crystal X-ray diffraction, SCXRD）分析表明，该团簇为四核结构，通过μ2-(1,1-叠氮)与μ3-(1,1,1-叠氮)桥联方式连接。该镍四核团簇在0.25 M醋酸盐缓冲电解液（pH=3.8）中表现出优异的析氢反应（hydrogen evolution reaction, HER）电催化活性与稳定性：在10 mA cm–2电流密度下仅需287 mV的低过电位，具备较高的双层电容（double-layer capacitance, Cdl）（0.34 mF cm–2）与较低的电荷转移电阻（17.6 Ω）。其本征参数如塔菲尔斜率（Tafel slope）为316 mV dec–1、周转频率（turnover frequency, TOF）在350 mV下为1.82 s–1、交换电流密度为0.002 A cm–2，均与该镍四核团簇阴极的析氢反应电催化活性相匹配。该电极在恒电流密度−10 mA cm–2下可稳定运行超过25 h，在0.25 M醋酸盐缓冲电解液中制氢的法拉第效率（Faradaic efficiency）超过92%。综合所有电化学分析结果可知，该镍四核团簇具备更优异的制氢活性、效率与可持续性，有望成为能源转换领域极具应用前景的候选催化剂。