Ultralow loading FeCoNi alloy nanoparticles decorated carbon mat for hydrogen peroxide reduction reaction and its application in direct ethylene glycol fuel cells

Hydrogen peroxide has been an attractive oxidant in direct liquid fuel cells. However, hydrogen peroxide reduction reaction heavily relies on noble metal-based electrocatalysts. In this work, a carbon mat decorated with FeCoNi alloy nanoparticles (namely FeCoNi/CM) of an ultralow loading, that is, 0.146 mg cm⁻², for hydrogen peroxide reduction is designed, fabricated, and applied as a free-standing cathode in a passive alkaline-acid direct ethylene glycol fuel cell. A piece of Pd/C coated carbon cloth (1.0 mg cm⁻²) is used as the anode and a pre-treated Nafion 211 membrane as the membrane. This passive fuel cell yields a peak power density of 17.4 mW cm⁻² at 23°C, which is comparable to an Au/C-based cathode (17.0 mW cm⁻²). The new electrode shows significantly enhanced mass transfer and allows a current density of 60.0 mA cm⁻², which is 1.5 times the value achieved with the Au/C-based cathode. This can be attributed to the much thinner thickness of FeCoNi/CM (50.0 μm) than Au/C-based cathode (380.0 μm). With the thinner thickness, the oxygen derived from the self-decomposition of hydrogen peroxide can be effectively removed from the cathode, which is beneficial for the transport of hydrogen peroxide to the catalyst surface. Moreover, with the use of this free-standing cathode, the passive fuel cell attains a continuous operation at a constant discharging current of 20.0 mA for more than 9 h, exceeding the 5 h achieved with the Au/C-based cathode at the same discharging current density.