Metal−nitrogen carbon (M−N−C) catalysts, atomically dispersed and nitrogen-coordinated MN x sites embedded in carbon planes, have exhibited encouraging oxygen reduction reaction activity in an acidic environment. However, one challenge for these materials is their insufficient long-term stability in the acid environment. Herein, we systematically investigate both catalytic activity toward ORR and stability under acid conditions using density functional theory (DFT). Various local atomic structures around the MN x site and different metal atoms (M = Cr, Mn, Fe, Co, Ni, and Ru) are considered in this study to understand the relation between atomic structures, stability, and catalytic activity. The stability of the M−N−C catalyst is considered from the propensity of the metal atom center to dissolve from the carbon host structure. The calculations reveal that the considered MN x sites are thermodynamically unstable in acid ORR conditions. However, based on the calculated thermodynamic driving force toward the metal dissolution, the MN 4 sites with Fe, Co, Ni, and Ru metal atoms embedded on the graphene plane and at the graphene edge are more stable in the acid ORR condition than the other considered MN x structures. Combining the stability and catalytic activity descriptor, we propose some acid-stable and active MN x structures toward ORR. This computational study provides helpful guidance for the rational modification of the carbon matrix hosting MN x moieties and the appropriate selection of a metal atom for optimizing the activity and stability toward the ORR reaction.

The development of an efficient electrocatalyst for the oxygen reduction reaction (ORR) is essential for the commercialization of fuel‐cell technologies. Iron carbide encapsulated in N‐doped graphene (NG/Fe3C) has been recognized recently as a promising ORR catalyst. In this study, the stability and catalytic activity of N‐doped graphene supported on metal–iron carbide (NG/M_Fe3C) toward the ORR are investigated by using DFT calculations. The NG/M_Fe3C heterostructure is modeled by substituting Fe atoms in the Fe3C substrate near the NG/Fe3C interface by metal atoms M (M=Cr–Mn, Co–Zn, Nb–Mo, Ta–W). The calculations show that the introduction of the metal atoms M alters the work function of the overlayer N‐doped graphene, which is found to correlate with the binding strength of the ORR intermediates. The introduction of Ni or Co atoms at the interface improves the ORR activity of the NG/Fe3C and stabilizes the heterostructure. The ORR activity increases as the concentration of Ni or Co atoms near the interface increases, and the stable heterostructure is available in a wide range of substituted concentrations. These results suggest approaches to improve the ORR activity of NG/Fe3C catalysts.

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Polybenzimidazole doped with aqueous KOH has emerged as an attractive electrolyte system for high-rate alkaline water electrolysis since it combines high ion conductivity with low H2 permeability. The lifetime is, however, limited to a few weeks under operating conditions due to degradation modes leading to chain scission. In this work, the underlying degradation mechanisms are explored by monitoring the chemical changes of a series of small-molecule arylene-linked bis-benzimidazoles treated under extreme caustic conditions for nearly 6 months at 80 °C. Degradation products and degradation pathways are identified experimentally and supported by density functional theory calculations. Based on the experimental and theoretical data, it is suggested that the degradation mainly proceeds via the remaining fraction of neutral benzimidazole and that stability can be improved by increasing the degree of deprotonation along the molecule.

A single metal site incorporated in N-doped carbon (M/N/C) is a promising electrocatalyst. Here, we perform a computation investigation of the effect of electrolyte anion adsorption on the activity and stability of single-atom catalysts (MN4) with M as transition metal and p-block metal. The MN4 site on two different graphene structures (bulk graphene and graphene edge) is studied under electrochemical conditions for the oxygen reduction reaction (ORR) and the CO2 reduction reaction (CO2RR). Because of the two-dimensional nature of the catalyst, reaction intermediates and electrolyte ions can interact with both sides of the single-atom catalyst. As a result, the electrolyte anions compete with water and adsorbate on the single metal site, in some cases either poisoning or modifying the catalyst activity and thermodynamic stability. We find most electrolyte anions adsorbs on the single metal site under ORR conditions but not at the lower potentials for the CO2RR. Still, the adsorption of water and gas molecules can occur under CO2RR conditions. For example, under ORR conditions, the thermodynamic driving force of the *SO4-FeN4 site in the 0.1 M H2SO4 solution is about 0.47–0.56 eV lower than the *O-FeN4 site in water, depending on the local carbon structure. Additionally, the stabilization by electrolyte anions depends on the nature of the metal atom. Our study demonstrates the important role of electrolytes and the coordination environment for the activity and stability of the M/N/C catalyst.