Electronic Modulation\nof Interfacial Engineering Co<sub>2</sub>P@FeP-FeP<sub>4</sub> Nanoframe\nHeterostructures Boosting\nOverall Water Splitting

The\ndevelopment of bifunctional electrocatalysts using\nrenewable\nelectricity for sustainable green energy industrial production is\na potential method. As a result, numerous standard methodologies investigate\ndeveloping electrocatalysts that naturally alter the electronic structure\nand minimize kinetic barriers. This study developed a promising method\nfor engineering interfacial heterostructure nanoframes (Co<sub>2</sub>P/FeP-FeP<sub>4</sub>, hereafter denoted as CFP-8) deposited on nickel\nfoam using hydrothermal and low-temperature phosphorization techniques.\nHowever, the improved CFP-8 electrocatalyst was exposed to abundant\nactive sites and nanocrystals that remained intact. Importantly, P\nincorporation plays a crucial role in creating a P vacancy defect,\nwhich contributes to the thermodynamic favoring of the electrocatalysis\nof the oxygen evolution reaction (OER) and intrinsically enhances\nthe hydrogen adsorption-free energy in hydrogen evolution reactions\n(HERs), due to the interconnected arrangement of CFP-8 nanoframes\nvia the synergistic and strain-induced effect. Therefore, enclosed\nCFP-8 nanoframes demonstrate good performance and display low overpotential\nwith high current densities (HER, η<sub>10</sub> = 97 mV, η<sub>20</sub> = 131 mV, η<sub>50</sub> = 186 mV; OER, η<sub>10</sub> = 230 mV, η<sub>20</sub> = 247 mV, η<sub>50</sub> = 280 mV) with a minimal Tafel value of η<sub>10</sub> = 111\nmV/dec and η<sub>10</sub> = 74 mV/dec for HER and OER under\nalkaline medium, superior to benchmark electrocatalysts. Also, CFP-8\ndemonstrated remarkable stability over 50 h, utilizing chronoamperometry\n(CA) and chronopotentiometry (CP). In addition, an integrated electrolyzer\nusing CFP-8/NF electrodes (polymeric binder-free electrodes) delivered\na cell voltage of 1.65 V with a current density of 20 mA cm<sup>–2</sup> with accelerated kinetics and improved stability, outperforming\nPt/C (cathode)||RuO<sub>2</sub> (anode) for overall water splitting\nreactions (OWSRs). The coexistence of Co, Fe, and P elements may accelerate\nelectron and mass movement, improving the high current density electrocatalytic\nperformance. This method paves the way for further research into low-cost\ntransition metal-based phosphides for bifunctional energy applications.