Open-hollow porous carbon-supported NiCo dual single atom catalyst with hydrophilic surface for enhanced oxygen reduction and hydrogen evolution reaction

Abstract The pursuit of high-performance, platinum-free electrocatalysts for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is fundamentally limited by the challenges of inadequate intrinsic activity and poor accessibility of active sites in single atom catalysts. Herein, the bimetallic single-atom NiCo/nitrogen-doped carbon (NC)-tannic acid (TA) electrocatalyst with the unclosed hollow morphology was constructed by the modification of precursor. Within this structure, hierarchical porous architecture, and surface hydrophilicity synergistically enhance the exposure and accessibility of active sites. Theoretical calculations confirm that the introduction of Ni facilitates electron transfer from Co sites, resulting in a downshifted d-band center. This electronic configuration effectively mitigates the over-adsorption of reaction intermediates, thereby reducing the energy barriers for both reactions. In alkaline ORR test, NiCo/NC-TA outperformed Pt/C-20% in both activity and stability, achieving a half-wave potential of 0.896 V and retaining 98% of the current after 10 h durability testing. Moreover, NiCo/NC-TA-based Zn–air batteries delivered a high open-circuit voltage of 1.49 V, a specific capacity of 764.1 mAh·g−1, and long-term cycling stability. Notably, the catalyst also exhibited enhanced HER activity, with a low overpotential of 92 mV in alkaline media, matching Pt/C-20% performance at a current density of 120 mA·cm−2. This work provides an approach for designing electrocatalysts through the integration of porosity engineering and electronic synergy, which could be extended to other energy-related material systems.