Electrodeposited MnCo and MnNiCo Spinels for Anion Exchange Membrane Direct Ammonia Fuel Cell Cathodes: An Alternative to Platinum

Direct ammonia fuel cells (DAFCs) hold great promise as clean energy conversion devices due to their carbon-free exhaust, the high energy density and liquid-phase storability of ammonia, and use of an existing production and distribution infrastructure. When using the state-of-the-art anion exchange membranes, ammonia crossover from the cathode to the anode, can cause rapid decay in DAFC performance as the current density increases. Mixed metal oxides containing manganese-nickel-cobalt have emerged as NH₃ tolerant cathode catalysts but their systematic testing under variable loading conditions in DAFC is rarely reported. Here, we examine low-temperature DAFCs with electrodeposited platinum (Pt), manganese-cobalt (MnCo), and manganese-nickel-cobalt (MnNiCo) cathodes on Ni foam. To isolate cathodic effects, all cells use identical Pt on Ni Foam anodes with alkaline ammonia feeds. Structural characterization confirms defect-rich spinel coatings. MnCo achieves oxygen reduction reaction (ORR) performance comparable to Pt, sustaining higher load voltage with lower interfacial resistance and larger capacitance, while MnNiCo shows restricted performance and rapid voltage loss, indicating sluggish charge transfer and fewer active sites. These results identify electrodeposited MnCo on Ni foam as a promising, scalable PGM-free cathode for DAFCs and highlight compositional and mesostructural tuning as key levers to improve catalytic activity and device performance.