Manipulating the Electronic Properties of an Fe Single Atom Catalyst via Secondary Coordination Sphere Engineering to Provide Enhanced Oxygen Electrocatalytic Activity in Zinc-Air Batteries.

Oxygen reduction and evolution reactions are two key processes in electrochemical energy conversion technologies. Synthesis of nonprecious metal, carbon-based electrocatalysts with high oxygen bifunctional activity and stability is a crucial, yet challenging step to achieving electrochemical energy conversion. Here, an approach to address this issue: synthesis of an atomically dispersed Fe electrocatalyst (Fe/NCP) over a porous, defect-containing nitrogen-doped carbon support, is described. Through incorporation of a phosphorus atom into the second coordination sphere of iron, the activity and durability boundaries of this catalyst are pushed to an unprecedented level in alkaline environments, such as those found in a zinc-air battery. The rationale is to delicately incorporate P heteroatoms and defects close to the central metal sites (FeNP-OH) in order to break the local symmetry of the electronic distribution. This enables suitable binding strength with oxygenated intermediates. In situ characterizations and theoretical studies demonstrate that these synergetic interactions are responsible for high bifunctional activity and stability. These intrinsic advantages of Fe/NCP enable a potential gap of a mere 0.65 V and a high power density of 263.8 mW cm when incorporated into a zinc-air battery. These findings underscore the importance of design principles to access high-performance electrocatalysts for green energy technologies.