Spin-State Engineering in Co–N–C Catalysts Enables Efficient Bifunctional Oxygen Electrocatalysis

The spin state of metal centers is a pivotal yet underexploited descriptor for electrocatalysis. This challenge is acute in bifunctional oxygen electrocatalysts, where the desirable high-spin state for optimal intermediate adsorption on single-atom sites is difficult to achieve and further complicated by the concurrent need to stabilize co-existing metallic nanoparticles against sintering. We propose that geometric distortion can serve as a driver to simultaneously distort single-atom sites and suppress nanoparticle sintering. To demonstrate this, we developed a poly(ionic liquid)-confined ultrafast thermal shock synthesis. Applied to a cobalt–nitrogen–carbon system, this strategy induces geometric distortion in Co-N 4 moieties, triggering a low-to-intermediate-spin transition and simultaneously suppressing Co NP agglomeration. Combined spectroscopic, magnetic, and theoretical analyses confirm that this distortion downshifts the d-band center, optimizes orbital overlap with oxygen intermediates, and lowers reaction barriers. The optimized catalyst exhibits high bifunctional activity (ORR E 1/2 = 0.84 V; OER η = 366 mV at 20 mA cm −2 ), delivers a peak power density of 312 mW cm −2, and retains its structure after ∼1360 charge–discharge cycles in a zinc-air battery. This work establishes geometric-distortion-driven spin-state modulation as a generalizable and actionable design principle for advanced electrocatalysts.