Balancing Activity and Selectivity in Two‐Electron Oxygen Reduction through First Coordination Shell Engineering in Cobalt Single Atom Catalysts

The electrochemical two-electron oxygen reduction reaction (2e^- ORR) offers a potentially cost-effective and eco-friendly route for the production of hydrogen peroxide (H₂O₂). However, the competing 4e^- ORR that converts oxygen to water limits the selectivity towards hydrogen peroxide. Accordingly, achieving highly selective H₂O₂ production under low voltage conditions remains challenging. Herein, guided by first-principles density functional theory (DFT) calculations, we show that modulation the first coordination sphere in Co single atom catalysts (Co-N-C catalysts with Co-N_xO_4-x sites), specifically the replacement of Co-N bonds with Co-O bonds, can weaken the *OOH adsorption strength to boost the selectivity towards H₂O₂ (albeit with a slight decrease in ORR activity). Further, by synthesizing a series of N-doped carbon-supported catalysts with Co-N_xO_4-x active sites, we were able to validate the DFT findings and explore the trade-off between catalytic activity and selectivity for 2e^- ORR. A catalyst with trans-Co-N₂O₂ sites exhibited excellent catalytic activity and H₂O₂ selectivity, affording a H₂O₂ production rate of 12.86 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>m</mml:mi> <mml:mi>o</mml:mi> <mml:mi>l</mml:mi> <mml:mspace></mml:mspace> <mml:msubsup><mml:mi>g</mml:mi> <mml:mrow><mml:mi>c</mml:mi> <mml:mi>a</mml:mi> <mml:mi>t</mml:mi> <mml:mo>.</mml:mo></mml:mrow> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msubsup> <mml:msup><mml:mrow><mml:mi>h</mml:mi></mml:mrow> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msup> <mml:mspace></mml:mspace></mml:mrow> <mml:annotation>${mol\ {g}_{cat.}^{-1}{h}^{-1}{\rm \ }}$</mml:annotation> </mml:semantics> </mml:math> and an half-cell energy-efficiency of 0.07 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow> <mml:msub><mml:mrow><mml:mi>m</mml:mi> <mml:mi>o</mml:mi> <mml:mi>l</mml:mi></mml:mrow> <mml:mrow><mml:msub><mml:mi>H</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> <mml:mspace></mml:mspace> <mml:msubsup><mml:mi>g</mml:mi> <mml:mrow><mml:mi>c</mml:mi> <mml:mi>a</mml:mi> <mml:mi>t</mml:mi> <mml:mo>.</mml:mo></mml:mrow> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msubsup> <mml:mspace></mml:mspace> <mml:msup><mml:mrow><mml:mi>J</mml:mi></mml:mrow> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>1</mml:mn></mml:mrow> </mml:msup> </mml:mrow> <mml:annotation>${{mol}_{{H}_{2}{O}_{2}}\ {g}_{cat.}^{-1}\ {J}^{-1}}$</mml:annotation> </mml:semantics> </mml:math> during a 100-hours H₂O₂ production test in a flow-cell.