Transition Metal‐Cross‐Linked‐Starch Aerogel‐Derived Porous Carbon‐Based Monolithic Chainmail Electrodes for High‐Current‐Density and Durable Alkaline Water Splitting

Abstract A porous carbon‐based monolithic chainmail electrode, namely Co₂P@CSA, is fabricated via direct carbonization of Co²⁺‐cross‐linked‐starch aerogel (Co²⁺‐SA) followed by low‐temperature vapor phosphorization. During successive carbonization‐phosphorization, the SA framework is formulated into 3D hierarchically porous carbon membrane matrix comprising hollow open carbon microspheres while the cross‐linked Co species are converted into uniformly distributed carbon‐encapsulated Co₂P nanoparticles on carbon microspheres. Thanks to the high porosity, excellent electrolyte wettability, unique chainmail structure, and good mechanical strength, the monolithic Co₂P@CSA can be directly used as a binder‐free bifunctional electrocatalyst for alkaline water splitting, and it can afford a high current density of 100 mA cm⁻² for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at low overpotentials of 140.0 and 305.5 mV, respectively, with outstanding stability at 50 mA cm⁻² for >30 h. More significantly, an alkaline electrolyzer assembled using Co₂P@CSA achieves a current density of 100 mA cm⁻² for overall water splitting (OWS) at a cell voltage of 1.94 V with unit Faradaic efficiency and provides a high solar‐to‐hydrogen (STH) conversion efficiency of 13.4 % when driven by a commercial silicon solar cell. This work offers an effective strategy towards cost‐effective fabrication of high‐performance carbon‐based monolithic chainmail electrocatalysts for energy conversion reactions.