A comprehensive review of recent advances in the field of oxygen reduction electrocatalysis utilizing nonprecious metal (NPM) catalysts is presented. Progress in the synthesis and characterization of pyrolyzed catalysts, based primarily on the transition metals Fe and Co with sources of N and C, is summarized. Several synthetic strategies to improve the catalytic activity for the oxygen reduction reaction (ORR) are highlighted. Recent work to explain the active-site structures and the ORR mechanism on pyrolyzed NPM catalysts is discussed. Additionally, the recent application of Cu-based catalysts for the ORR is reviewed. Suggestions and direction for future research to develop and understand NPM catalysts with enhanced ORR activity are provided.

The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction. Iron-based non-precious metal catalysts exhibit promising activity and stability, as an alternative to state-of-the-art platinum catalysts. However, the identity of the active species in non-precious metal catalysts remains elusive, impeding the development of new catalysts. Here we demonstrate the reversible deactivation and reactivation of an iron-based non-precious metal oxygen reduction catalyst achieved using high-temperature gas-phase chlorine and hydrogen treatments. In addition, we observe a decrease in catalyst heterogeneity following treatment with chlorine and hydrogen, using Mössbauer and X-ray absorption spectroscopy. Our study reveals that protected sites adjacent to iron nanoparticles are responsible for the observed activity and stability of the catalyst. These findings may allow for the design and synthesis of enhanced non-precious metal oxygen reduction catalysts with a higher density of active sites.

Earth-abundant and inexpensive catalysts with low overpotential and high durability are central to the development of efficient water splitting electrolyzers. However, improvements in catalyst design and preparation are currently hampered by the lack of detailed understanding of the reaction mechanisms of the oxygen evolution reaction (OER) facilitated by non-precious metal (NPM) catalysts. In this manuscript, we conducted a kinetic isotope effect (KIE) study in an effort to identify the rate-determining step (RDS) of these intricate electrocatalytic reactions involving multiple proton-coupled electron transfer (PCET) processes. We observed an inverse KIE for OER catalyzed by Ni and Co electrodes. These results contribute to a more complete understanding of the OER mechanism and allow for the future development of improved NPM catalysts.

The development of non-precious-metal (NPM) catalysts to replace the Pt alloys currently used in fuel cells to facilitate the oxygen reduction reaction (ORR) is a vital step in the widespread utilization of fuel cells. Currently, the ORR mechanism for NPM catalysts is not well understood, prohibiting the design and preparation of improved NPM catalysts. We conducted a kinetic isotope effect (KIE) study to identify the rate-determining step (RDS) of this intricate electrocatalytic reaction involving multiple proton-coupled electron transfer (PCET) processes. We observed a KIE of about 2 for the ORR catalyzed by a NPM catalyst, which demonstrates that for these electrocatalysts protons are involved in the RDS during ORR. These results contribute to a more complete understanding of the ORR mechanism and suggest that the design of future NPM catalysts must include careful consideration of the role of protons during ORR.

After a brief review of anisotropy on the nanoscale, experiments in which nanorod core-shell-shell particles are grown are presented. These "nanomatryoshkas" consist of a gold nanorod core, a silica shell, and a final gold shell. Calculation of the near-field properties of these structures using the discrete dipole approximation uncovers the change in location of local electric fields upon gold outer shell growth. Electrochemical experiments of the weak reducing agents used to grow the gold nanorod cores suggest a correlation between the strength of the reducing agent and its ability to promote longer nanorod growth. The final nanostructures do not exhibit a smooth outer shell, unlike their spherical counterparts.