Dharmaraj, K.; Hanna, R.; Ruske, R.; Douglas-Henry, D.; Lauermann, I.; Prathapani, S.; Reyes-Figueroa, P.; Rodriguez-Ayllon, P.; Lu, Y.; Nicolosi, V.; Schlatmann, R.; Browne, M. P.; Menezes, P.W.; Calnan, S.: Ammonia tolerant alkaline oxygen reduction reaction on bimetallic cobalt spinels. Chemical Engineering Journal 522 (2025), p. 167192/1-11
10.1016/j.cej.2025.167192
Open Accesn Version
Abstract:
Ammonia, supported by its well-established transportation and distribution infrastructure, is considered as a promising carbon-free hydrogen carrier and emerging as an energy source via low-temperature anion exchange membrane direct ammonia fuel cells (AEM-DAFC). However, ammonia crossover from the anode can poison cathode catalysts, reducing oxygen reduction reaction (ORR) efficiency and cell voltage. Herein, to substitute the state-of-the-art catalyst, Pt/C, and to develop stable, ammonia-tolerant ORR catalysts, monometallic oxides of Co, Fe, Ni, Mn, and bimetallic M-CoOx (M = Fe, Ni, Mn) were synthesized on gas diffusion electrode (GDE) with microporous layer and tested for ORR activity. Among these, MnCoOx-1 (Mn:Co 1:2) demonstrated high NH3 tolerance and ORR activity comparable to benchmark fuel cell catalyst, Pt/C under GDE conditions. In-situ Raman spectroscopy performed under GDE conditions revealed that the structure of MnCoOx-1 remains stable, with no detectable changes, even at current densities as high as −25 mA cm−2. During the accelerated stress test conducted at 80 °C with 3.0 M NH3 in 3.0 M KOH and compressed air at 1.0 bar back pressure feed, MnCoOx-1 showed an overpotential increase of less than 50 mV at −500 mA cm−2 in a 1.0 cm2 membrane electrode assembly type GDE half-cell. Post-mortem X-ray analysis revealed a slight change in the relative atomic composition of MnCoOx-1 after the AST. This comprehensive study reveals that MnCoOx-1 is a stable NH3 tolerant ORR catalyst, making it a promising cathode candidate for low temperature AEM-DAFC applications.