Redox potential-engineered heteropolyacid regenerative fuels for emission-free direct liquid fuel cells

Abstract

To address the sluggish oxidation kinetics, noble metal dependency, and carbon emissions of traditional direct liquid fuel cells (DLFCs), this study proposes a novel strategy utilizing Keggin-type heteropolyacids (HPAs) as recyclable fuels. Through a systematic comparison of the electrochemical properties of phosphotungstic acid ({PW₁₂}), silicotungstic acid ({SiW₁₂}), and cobaltotungstic acid ({CoW₁₂}), combined with density functional theory (DFT) calculations, we elucidate the regulatory mechanism of central atom valence states and proton–electron coupling effects on redox potential distribution. The results reveal that {CoW₁₂}, owing to the low-valent Co(II) center and proton-coupled electron transfer mechanism, exhibits a significantly concentrated four-electron reduction potential range (−0.035 to −0.151 V vs. SHE), effectively suppressing hydrogen evolution side reactions and enabling full electron utilization. Experimental validation demonstrates that the {CoW₁₂}-based DLFC achieves an energy density of 27.2 Wh L⁻¹ and a peak power density of 0.529 W cm⁻² at 0.58 V at ambient temperature and under non-humidified conditions and anode noble metal-free operation, representing 118% and 46% improvements over the reported {PW₁₂} system, respectively. The system also demonstrates stable discharge performance over 30 hours. This work provides a theoretical foundation and material innovation paradigm for designing high-capacity, low-cost heteropolyacid-based fuel cell systems.