Infant diaper waste-derived multifunctional MoN-Ni3C@CFs for full water splitting at neutral and alkaline pH and solar-to-hydrogen conversion: a win–win combination†

Abstract

Molybdenum nitride-nickel carbide nanocarbon fibers (MoN-Ni₃C@CFs) are efficient electrocatalysts for overall water splitting. These catalysts consist of MoN and Ni₃C dispersed on a carbon support derived from infant-urinated disposable diapers, enabling sustained exposure of active sites and high matrix conductivity. The MoN-Ni₃C@CFs synthesized from a simple win–win incineration strategy exhibited bifunctional active sites (OER/HER: 211/132 mV) for water dissociation as well as adsorption/desorption of intermediates. Operando electrochemical impedance spectroscopy (EIS) analysis revealed that MoN-Ni₃C@CFs exhibit lower charge transfer resistance and enhanced kinetics compared to NiMoO₄. This may be attributed to the etching of pore forming additives by CFs during the electrocatalytic process. The incorporation of CFs modified the surface area as well as the porosity of MoN-Ni₃C@CFs, facilitating an electrocatalytic proton-decoupled electron transfer mechanism during OER. The improved activity was further supported by Bode analysis at various potentials. The temperature-dependent analysis indicated that the activated carbon in MoN-Ni₃C@CFs decreased the activation energy (3.14 kJ mol⁻¹) by three times, as compared to that of MoN-Ni₃C@CFs (9.29 kJ mol⁻¹). The high faradaic efficiency indicates excellent selectivity of MoN-Ni₃C@CFs. The total cell and solar cell-driven electrolyzer MoN-Ni₃C@CFs^(+,–) exhibited exceptional overall water-splitting efficiency (1.56 V at 10 mA cm⁻²), establishing the suitability for practical applications. Furthermore, an alternative process with MoN-Ni₃C@CFs was used to produce carbon-negative green H₂ and also used for value-added electrolysis, thereby exploiting economic benefits to convert waste into renewable resources. The CFs etching strategy, a new synthetically simple approach, can also be employed for pore augmentation to boost the catalytic performance.