This work analyzes the optimization
of a potential Pt-free cathode
fuel cell catalyst, an iron phthalocyanine monolayer supported on
a graphene substrate (GFePc) by regulating the eg orbital
filling states via substrate doping and/or ligand exchange. In the
present work, the substrate doping (B-doping and N-doping) of graphene
and/or ligand exchanges (F– and NH2−) of
FePc are explored to tune the performance of GFePc using ab initio
spin-polarized density functional theory (DFT) calculations. The catalytic
steps for the dominating pathway for GFePc (associative mechanism)
were approximated for the entire oxygen reduction reaction (ORR),
followed by the subsequent water formation reaction (WFR). The rate-limiting
step of the mechanism is the initial reduction of O2 to
the O–OH reaction. The DFT results show that in a water-solvated
environment boron doping of ∼1 atom % of graphene lowers the
overpotential of the rate-limiting step to ∼0.49 eV, which
is on par with the Pt cathode, at normal fuel cell operating conditions.
This work also reveals that the scaling relationship can be broken
via substrate doping and/or via ligand exchange for superior ORR activity,
and this will guide the development of single-metal atom-based next-generation
Pt-free fuel cell cathode catalysts.
Finding a platinum‐free cathode catalyst that effectively models the oxygen reduction reaction (ORR) of a proton‐exchange membrane (PEM) fuel cell cathode better than the current commercial Pt/C catalyst has been a major shortcoming in fuel cell technology. Overall, a promising platinum‐free cathode catalyst must offer great ORR activity, ORR selectivity, and acid stability. Due to their enticing ORR activity and selectivity to the preferred four‐electron ORR pathway, the possible dissolution reactions and oxygen‐intermediate reactions of iron phthalocyanine monolayer supported on a pristine graphene (GFePc) and boron‐doped graphene substrate (BGFePc) have been studied to determine the stability as a function of potential and pH through spin‐polarized density functional theory (DFT) calculations at both infinitesimally low (10−9 m) and 1 m Fe2+/Fe3+ ionic concentrations. BGFePc offers higher stability in both concentrations than GFePc. In both cases, the oxygen‐intermediates are more stable than the bare catalytic surface due to the metal d‐band center shifting further away from the Fermi level in the valence band state (higher energy of antibonding). Moreover, at an Fe2+ ionic concentration, both catalysts would be stable in the potential and pH regions at the operating conditions of rotating disk electrode (RDE) experiments and PEM fuel cells.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.