Optimized electronic structure induced by cobalt metaphosphate/phosphide for highly efficient hydrazine-assisted water splitting at high current densities.

Hydrazine oxidation reaction (HzOR) emerges as a superior alternative to the sluggish oxidation reaction (OER) due to the ultralow thermodynamic potential. Herein, abundant CoPO/CoP heterostructures were constructed in N-doped carbon (denoted CoPO/CoP@NC) derived from the waste cigarette butts through the carbonization and subsequent phosphorization process. Owing to the hierarchically wave-like architecture, well-defined electron transfer pathway, and strong interfacial coupling between CoPO and CoP, CoPO/CoP@NC expressed outstanding electrocatalytic performance, requiring ultralow potentials of -207 and 91 mV at a large current density of 500 mA cm for the hydrogen evolution reaction (HER) and HzOR, respectively. When integrated into a hydrazine-assisted water electrolysis as both electrodes, the device required only 0.79 V to drive 500 mA cm, significantly lower than that for traditional water electrolysis. Density functional theory (DFT) calculations revealed that the presence of CoPO optimized the energy barriers of crucial reaction intermediates and accelerated the reaction kinetics for HER and HzOR effectively. Furthermore, an innovative and economic parallel integrated system, entirely driven by solar energy, was proposed as a concept for successive energy-saving hydrogen. This work provides a promising and pragmatic path for energy-efficient hydrogen generation and high-value reutilization of cigarette butt simultaneously.