Tiny changes at the atomic scale can determine the future of clean energy. In a new study, Tohoku University researchers have revealed how the precise coordination environment surrounding a single cobalt atom dramatically influences its catalytic behavior in the oxygen reduction reaction (ORR)―a key process in fuel cells and sustainable hydrogen peroxide production.

Single-atom metal-nitrogen-carbon (M-N-C) catalysts are attracting attention as cost-effective alternatives to platinum-based materials. Yet understanding exactly how the number and arrangement of nitrogen atoms bound to the metal center affect activity has remained a long-standing challenge, largely due to the difficulty of synthesizing catalysts with precisely defined structures.

To overcome this barrier, the team constructed a series of heterogeneous molecular catalysts by depositing structure-defined organometallic cobalt complexes onto catalytically inert carbon nanotube substrates. This strategy enabled strict control over first-shell coordination numbers, producing Co-Nx active sites with x = 3, 4, and 5.

Four molecular precursors with distinct ligand symmetries were selected to systematically tune the cobalt coordination environment. By comparing asymmetric and symmetric structures, the researchers were able to directly correlate atomic configuration with catalytic performance.

Electrochemical measurements revealed striking differences. Asymmetric Co-N3 sites exhibited enhanced overall ORR activity, while lower-symmetry Co-N5 centers achieved the highest selectivity toward the two-electron pathway, favoring hydrogen peroxide production. In contrast, symmetric Co-N4 configurations showed comparatively lower activity.

Density functional theory (DFT) calculations closely matched experimental results, validating the proposed structure-activity relationships. The findings demonstrate that even subtle variations in coordination symmetry significantly alter reaction energetics and product selectivity.

Operando spectroscopic studies and kinetic analyses further uncovered that coordinating carbon or nitrogen atoms in asymmetric Co-N3 and Co-N5 sites can become protonated during operation, acting as proton relays. This dynamic participation of the coordination shell provides a mechanistic explanation for their superior catalytic performance.

"Our work shows that catalytic performance is not determined solely by the metal atom itself, but by the architecture of its immediate coordination environment," said Hao Li, a Distinguished Professor at Tohoku University's WPI-AIMR. "By precisely designing that environment, we can tune activity and selectivity for renewable energy technologies."

All experimental and computational data from the study have been made openly available through the Digital Catalysis Platform, supporting transparency and accelerating catalyst innovation. The insights gained here offer a powerful design principle for next-generation single-atom electrocatalysts in sustainable energy conversion.

The findings were published in the Journal of the American Chemical Society on February 6, 2026.