Building P-Poor Ni2P and P-Rich CoP3 Heterojunction Structure with Cation Vacancy for Enhanced Electrocatalytic Hydrazine and Urea Oxidation

Handling hydrazine/urea wastewater through electrochemical oxidation technology (HzOR/UOR) holds significant importance for sewage disposal and nitrogen recycling, as the presence of hydrazine/urea leads to severe environmental issues . On the other hand, hydrazine/urea could potentially serve as a new type of fuel. However, at present, this remains a considerable challenge. The development of a low-cost, highly efficient, and stable electrocatalyst stands as a prerequisite for achieving this goal. In this study, a novel Ni 2 P/CoP 3 -Zn vac bimetallic phosphide catalyst is designed and constructed using a hydrothermal-alkali etching-phosphating three-step method. This catalyst integrates P-rich CoP 3 , P-poor metallic Ni 2 P, and abundant Zn 2+ cation vacancies into a single structure for HzOR/UOR. Copious P in CoP 3 provides a wealth of negative electrons, which aids in the adsorption of positive reactive intermediates. Meanwhile, P-poor metallic Ni 2 P exhibits excellent electrical conductivity , ensuring rapid reaction dynamics. Both physical and electrochemical experiments confirm the successful creation of the Ni 2 P/CoP 3 -Zn vac heterojunction , along with the distinctive electron structure of Ni 2 P and CoP 3 . Electron paramagnetic resonance (EPR) results validate the presence of cation vacancies, which significantly enhance the density of active sites. Consequently, this innovative Ni 2 P/CoP 3 -Zn vac heterojunction catalyst displays remarkable electrocatalytic activity , achieving a potential of −47 mV/1.311 V to attain 10 mA·cm −2 for HzOR and UOR , respectively. The Tafel slopes of 54.3 and 37.24 mV·dec −1 for HzOR and UOR are significantly smaller than those of single-phased Ni 2 P and CoP 3 , as well as the two-phased phosphide without alkali etching. Building upon the excellent HzOR/UOR performance of the Ni 2 P/CoP 3 -Zn vac heterojunction, a two-electrode cell for direct hydrazine fuel cells (DHzFC) and direct urea-hydrogen peroxide fuel cells (DUHPFC) is assembled with a Ni 2 P/CoP 3 -Zn vac anode. This configuration demonstrates a maximum power density of 229.01 mW·cm −2 for DHzFC and 16.22 mW·cm −2 for DUHPFC. Moreover, both DHzFC and DUHPFC exhibit exceptional stability for up to 24 h. A homemade aqueous Zn-Hz battery, equipped with a Ni 2 P/CoP 3 -Zn vac cathode, further demonstrates its practicality for energy conversion. This work underscores a promising avenue for developing cost-effective and highly stable solutions for UOR and HzOR. The P-poor Ni 2 P and P-rich CoP 3 heterojunction structures with massive cation vacancy deliver outstanding electro-oxidation activity toward hydrazine and urea.