Electronic modulation of MOF-engineered bimetallic phosphides for cost-effective ampere-level water splitting and continuous hydrogen production via supercapacitor integration

Abstract

Engineering a phosphide-based multifunctional heterostructure with high redox activity, stability, and efficient charge kinetics for both supercapacitors and water splitting remains challenging due to sluggish reaction kinetics and structural instability. This study overcomes these challenges by implementing a rapid, energy-efficient approach to develop a MOF-modulated MnP@Cu₃P heterostructure via a hydrothermal process followed by high-temperature phosphorization. The heterostructure demonstrates superior redox activity with enhanced stability and improved charge kinetics achieving a high specific capacity of 1131 C g⁻¹ as supported by density functional theory findings of increased DOS near the Fermi level. The flexible supercapacitor achieves a peak energy density of 99.20 Wh kg⁻¹ and power density of 15.40 kW kg⁻¹. Simultaneously, it shows exceptional hydrogen evolution reaction performance with an overpotential of η₁₀ = 44 mV and η₁₀₀₀ = 225 mV, attributed to electron transfer from Cu to Mn via P bridging, which shifts the active centers from Mn and Cu sites to the P site, confirmed by lowest ΔG_H* value of −0.16 eV. The overall water-splitting in full-cell electrocatalyzer delivers cell voltage of E₂₀ = 1.48 V and E₁₀₀₀ = 1.88 V and setting a new standard in solar-to-hydrogen efficiency of 20.02%. The electrolyzer cell maintained prolonged stability at industrial-scale current densities of 1.0 A cm⁻² under alkaline electrolysis achieving an estimated hydrogen production cost of INR 146.7 or US$ 1.67 per kilogram aligning with the cost target of $ 2/kg by 2026 established by the Clean Hydrogen Electrolysis Program, U.S. department of energy. Furthermore, real-phase demonstration highlights the uninterrupted hydrogen production till 6-minutes via connecting this electrocatalyzer with photovoltaic-charged supercapacitors effectively addressing solar intermittency and gas fluctuations challenges in water-electrolysis.