Preparation Of Self-supported Cobalt Phosphide Composites For Electrocatalytic Water Splitting

Hydrogen production technology is crucial for hydrogen energy development.As a typical energy conversion reaction,water splitting requires a catalyst to reduce the activation barrier.Although noble metal catalysts have excellent performance,they are limited by cost.Therefore,non-noble metal catalysts with lower cost and excellent performance are promising.Among them,the composite catalyst supported by metal foam avoids the introduction of adhesive,and the porous structure and high electrical conductivity can effectively promote the reaction.In view of this,the synthesis and electrocatalytic performance of self-supported cobalt phosphide composites are investigated in this paper.The main conclusions are as follows:（1）Fe P-modified Co₂P electrocatalysts（Fe P/Co₂P-WO_x/NF）were prepared through immersion and phosphorylation using WO_x/NF as a self-supporting electrode for efficient alkaline overall water splitting.Overpotentials of 143 m V and 180 m V were required for HER and OER to reach a current density of 10 m A cm^-2 under 1 M KOH alkaline solution,respectively.Meanwhile,the slopes of Tafel curves are 85.7 m V dec^-1 and 61.1 m V dec^-1.In addition,a cell voltage of only 1.51 V is required to drive a current density of 10 m A cm^-2.The excellent catalytic properties are attributed to the self-supported composites providing a large number of active sites,facilitating charge transfer and optimizing hydrophilicity.The synergistic effects of the bimetallic phosphide modulates the H adsorption energy of the catalyst as well as the adsorption energy of the oxygen-containing intermediates.（2）The construction of nanostructures can effectively improve the catalytic specific surface area and active sites.Ni-MOF/NF precursors were synthesized by etching NF,and ZIF-67 was subsequently grown on Ni-MOF nanosheet,which was reconstructed after phosphorylation to form Ni Co P nanorods（Ni Co P/NF）for efficient hydrogen generation.The Ni-MOF nanosheet provided a good carrier for the growth of ZIF-67.Thus the obtained Ni Co P/NF resulted in increase in the bilayer capacitance from 2.6 m F cm^-2 for Ni-MOF/NF to 7.3 m F cm^-2 for Ni Co P/NF and reduction the charge transfer resistance to 0.65Ω.Benefiting from the reconfiguration of Ni-MOF and ZIF-67 to form nanorods during phosphorylation,the active area of the catalyst was greatly increased to optimize the catalystic performances.The Ni Co P/NF shows a good overpotential of 183m V by ensuring more sites for rapid charge transfer in the reaction.（3）Co-MOF/NF was firtly hydrothermally synthesized using NF as the substrate,and then the C layer was incorpoerated by using melamine as the carbon source to prepare the C@Co O/NF support electrode.The sandwich structure Co P@C@Co O/NF was synthesized by phosphating the electrodeposition of Co（OH）₂ on C@Co O/NF.The buffering effect of the C layer facilitated the stable growth and structure stabilization of Co P.The catalyst exhibited a low overpotential of 88 m V for HER at a cathodic current density of 10 m A cm^-2,as well as a reduced Tafel slope of 88.7 m V dec^-1 and a good catalytic stability（94%）at high current densities.The sandwich structure constructed by carbon incoperation favors the increase of active sites,enhancement of electron transport and interfacial modulation of H adsorption to achieve excellent catalytic performance.In brief,a series of cobalt phosphide self-supported electrode catalysts were prepared for water splitting.The self-supported structures are significantly beneficial for the increase of catalyst surface area and the promotion of electron transfer.The interfacial and synergistic effects of the composites endows the improvement in electrocatalytic performance as well.