Enhanced Water\nSplitting Electrocatalysis with Heterointerfacial\nCobalt Phosphide In Situ Supported on a Cellulose-Derived Carbon Aerogel

The\nactive site density, intrinsic activity, and supporting substrate\nof cobalt phosphide catalysts are vital to their performance in alkaline\nwater electrolysis. In this work, a CoP/Co<sub>2</sub>P loaded on\ncellulose nanofiber-derived carbon aerogels (CP/CCAs) bifunctional\nelectrocatalyst with a three-dimensional network and heterostructure\nis illustrated through sequential facile hydrothermal, freeze-drying,\nand phosphorylation processes. The three-dimensional network of carbon\naerogels derived from cellulose nanofibers reveals a specific surface\narea of 183.41 m<sup>2</sup>/g, greatly enriching the active sites\nand facilitating the electron and mass transportation. Besides, interactions\nbetween CoP/Co<sub>2</sub>P with a heterogeneous structure and carbon\naerogels modulate the electronic structure to enhance the intrinsic\nactivity of the catalysts. Benefiting from these advantages, CP/CCAs-2\ndemonstrates a superior oxygen evolution reaction activity (η10\nmA cm<sup>–2</sup> = 277 mV) over the benchmark RuO<sub>2</sub> and a moderate hydrogen evolution reaction performance (η10\nmA cm<sup>–2</sup> = 63 mV). Density functional theory calculations\nfurther reveal that the coupling of CoP/Co<sub>2</sub>P and cellulose-derived\ncarbon aerogels promotes the water adsorption and activates the H–O\nbond. As a result, the alkaline electrolyzer assembled with CP/CCAs-2\nboth as a cathode and an anode shows a low cell voltage of 1.59 V\nat a current density of 10 mA cm<sup>–2</sup> and good stability.\nThis work provides a strategy for phosphide electrocatalysts composited\nwith green carbon carriers for overall water splitting.