Ultradense carbon-encapsulated Co2P chainmail catalyst embedded within hierarchically porous monolithic carbon matrix for superior alkaline electrocatalytic water splitting

While carbon-encapsulated transition metal-based chainmail electrocatalysts in powdery forms have shown impressive electrocatalytic activity toward water splitting, their performance is often restricted by the insufficient catalytic active sites and stability. Herein, a monolithic carbon-based bifunctional electrocatalyst is fabricated by embedding ultradense N, P-codoped carbon-encapsulated Co2P nanoparticles (<50 nm) within hierarchically porous carbonized Pleurotus eryngii (Co2P@NPC/CPE). The integrated porous structure of Co2P@NPC/CPE electrode contributes to fast multiphase mass diffusion and electron transfer. Moreover, the ultradense Co2P@NPC chainmail catalyst offers abundant active sites and strong interfacial coupling with CPE matrix thus ensuring excellent structural stability. These merits endow the Co2P@NPC/CPE with low overpotentials of 173 and 349 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at 100 mA cm−2 in 1.0 M KOH, respectively, and it retains 77 % and 74 % of the HER and OER activities after 100 and 10 h, respectively. Notably, a two-electrode electrolyzer assembled with Co2P@NPC/CPE requires lower cell voltages of 1.66 and 1.92 V at 10 and 100 mA cm−2, respectively, while demonstrating 76 % retention of its initial activity after 12 h at 100 mA cm−2 and providing a high solar-to-H2 conversion efficiency of 18 % under AM 1.5G irradiation from a Si solar cell.