Regulating local coordination environment of Mg -Co single atom catalyst for improved direct methanol fuel cell cathode

Fuel cells operated with a reformate fuel such as methanol are promising power systems for portable electronic devices due to their high safety, high energy density and low pollutant emissions. However, several critical issues including methanol crossover effect, CO-tolerance electrode and efficient oxygen reduction electrocatalyst with low or non-platinum usage have to be addressed before the direct methanol fuel cells (DMFCs) become commercially available for industrial application. Here, we report a highly active and selective Mg -Co dualsite oxygen reduction reaction (ORR) single atom catalyst (SAC) with porous N-doped carbon as the substrate. The catalyst exhibits a commercial Pt/C-comparable half-wave potential of 0.806 V (versus the reversible hydrogen electrode) in acid media with good stability. Furthermore, practical DMFCs test achieves a peak power density of over 200 mW cm -2 that far exceeds that of commercial Pt/C counterpart (82 mW cm -2 ). Particularly, the Mg -Co DMFC system runs over 10 h with negligible current loss under 10 M concentration methanol work condition. Experimental results and theoretical calculations reveal that the N atom coordinated by Mg and Co atom exhibits an unconventional d -band-ditto localized p -band and can promote the dissociation of the key intermediate *OOH into *O and *OH, which accounts for the near unity selective 4e - ORR reaction pathway and enhanced ORR activity. In contrast, the N atom in SAC -Co remains inert in the absorption and desorption of *OOH and *OH. This local coordination environment regulation strategy around active sites may promote rational design of high-performance and durable fuel cell cathode electrocatalysts.& COPY; 2023 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) Peer review under responsibility of Chongqing University

Automated summary

Fuel cells operated with a reformate fuel such as methanol have several critical issues that need to be addressed before they can be commercially available, including methanol crossover effect, CO-tolerance electrode, and efficient oxygen reduction electrocatalyst. A highly active and selective Mg-Co dualsite oxygen reduction reaction (ORR) single atom catalyst with porous N-doped carbon as the substrate is reported here, showing promising performance and stability. This research provides insights into the design of high-performance and durable fuel cell cathode electrocatalysts.