The electrochemical synthesis of azo-bridged nitrogen-rich heterocyclic compounds has emerged as a promising strategy in the field of energetic materials due to its efficiency and controllability. Here, we present an innovative and environmentally benign electrocatalytic strategy employing cobalt phosphide (Co2P) nanowire arrays as cathodic catalysts for the safe and efficient synthesis of sodium 5,5′-azo-tetrazole under mild electrochemical conditions. Notably, the Co2P catalyst drives the reaction at a low potential of −0.4 V (vs Hg/HgO), which benefits from its unique needle-like morphology that optimizes electron transport pathways and active site distribution. By adjustment of the applied potential and reaction time, the yield of the reductive coupling can be effectively controlled. A detailed mechanistic pathway has been elucidated for the cathodic reductive coupling of sodium 5-nitrotetrazole mediated by Co2P electrodes. Electrochemical reduction at −0.6 V (vs Hg/HgO) and −0.8 V (vs Hg/HgO) yields a tunable mixture of sodium 5,5′-azo-tetrazole and its azoxy derivative, whereas exclusive generation of sodium 5,5′-azo-tetrazole is achieved at −1 V (vs Hg/HgO) through precise modulation of electron transfer kinetics. This voltage-gated synthesis paradigm establishes a novel electrochemical methodology for the programmable assembly of nitrogen-rich heterocyclic frameworks, offering unprecedented control over azo-linkage formation in energetic material design.
Splitting water to produce hydrogen through an efficient and low-cost way requires the development of catalysts based on earth-abundant elements. Among transition metal phosphides, bimetal phosphides demonstrate superior hydrogen evolution reactivity to monometal phosphides. Therefore, we synthesized Ni2P–Co2P nanowire arrays on nickel foam with excellent catalytic performance by hydrothermal and low-temperature phosphorization. In 1 M KOH, the catalyst demonstrates low overpotentials of 99 and 161 mV to reach current densities of 10 and 100 mA cm–2, respectively. In 0.5 M H2SO4, the overpotentials of Ni2P–Co2P are only 94 and 159 mV at current densities of 10 and 100 mA cm–2, respectively. In a neutral solution, the overpotentials of the catalyst are also only 146 and 309 mV at current densities of 10 and 100 mA cm–2, respectively. The Tafel slopes of Ni2P–Co2P are only 53.1, 48.26, and 138.3 mV dec–1 in acid, alkaline, and neutral solutions, respectively. Moreover, the outperformance of its durability was tested for 20 h in acid and alkaline solutions, which maintained a stable current density of 10 mA cm–2. This work demonstrates a feasible route to design transition metal phosphides used in pH-universal HER electrocatalysts.
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