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 Ni2P/CoP3-Znvac bimetallic phosphide catalyst is designed and constructed using a hydrothermal-alkali etching-phosphating three-step method.This catalyst integrates P-rich CoP3,P-poor metallic Ni2P,and abundant Zn2+cation vacancies into a single structure for HzOR/UOR.Copious P in CoP3 provides a wealth of negative electrons,which aids in the adsorption of positive reactive intermediates.Meanwhile,P-poor metallic Ni2P exhibits excellent electrical conductivity,ensuring rapid reaction dynamics.Both physical and electrochemical experiments confirm the successful creation of the Ni2P/CoP3-Znvac heterojunction,along with the distinctive electron structure of Ni2P and CoP3.Electron paramagnetic resonance(EPR)results validate the presence of cation vacancies,which significantly enhance the density of active sites.Consequently,this innovative Ni2P/CoP3-Znvac 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 Ni2P and CoP3,as well as the two-phased phosphide without alkali etching.Building upon the excellent HzOR/UOR performance of the Ni2P/CoP3-Znvac heterojunction,a two-electrode cell for direct hydrazine fuel cells(DHzFC)and direct urea-hydrogen peroxide fuel cells(DUHPFC)is assembled with a Ni2P/CoP3-Znvac 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 Ni2P/CoP3-Znvac 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.
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