Microkinetic Modelling of Electrochemical Oxygen Evolution Reaction on Ir(111)@N‐Graphene Surface

We have explored the thermodynamics and microkinetic aspects of oxygen evolution catalysis on low loading of Ir(111) on nitrogen-doped graphene at constant potential. The electronic modification induced by N-doping is the reason for the reduced overpotential of OER. The N-induced defect in the charge density is observed with increasing charge-depleted region around the Ir atoms. The lattice contraction shifts the d-band center away from the Fermi level, which increases the barrier for OH* and O* formation on Ir(111) supported on NGr (Ir(111)@NGr). Thus, highly endothermic O* formation reduces the OOH* formation, which is the potential determining step. For comparison, all electronic and binding energy calculations were also performed against Ir NP supported on Gr (Ir(111)@Gr). The stepwise potential-dependent activation barrier ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>G</mml:mi> <mml:mi>a</mml:mi></mml:msub> <mml:annotation>${{G}_{a}}$</mml:annotation> </mml:semantics> </mml:math> ) was obtained using the charge extrapolation method. The third step remains the RDS in all ranges of water oxidation potentials. The potential dependent <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>G</mml:mi> <mml:mi>a</mml:mi></mml:msub> <mml:annotation>${{G}_{a}}$</mml:annotation> </mml:semantics> </mml:math> is further applied to the Eyring rate equation to obtain the current density ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>j</mml:mi> <mml:mrow><mml:mi>O</mml:mi> <mml:mi>E</mml:mi> <mml:mi>R</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${{j}_{OER}}$</mml:annotation> </mml:semantics> </mml:math> ) and correlation between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>j</mml:mi> <mml:mrow><mml:mi>O</mml:mi> <mml:mi>E</mml:mi> <mml:mi>R</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${{j}_{OER}}$</mml:annotation> </mml:semantics> </mml:math> and pH dependence, i. e., OH^- concentration. The microkinetic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>j</mml:mi> <mml:mrow><mml:mi>O</mml:mi> <mml:mi>E</mml:mi> <mml:mi>R</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${{j}_{OER}}$</mml:annotation> </mml:semantics> </mml:math> progression leads to a Tafel slope value of 30 mV dec^-1 at pH=14.0, requiring <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>η</mml:mi> <mml:mrow><mml:mi>k</mml:mi> <mml:mi>i</mml:mi> <mml:mi>n</mml:mi> <mml:mi>e</mml:mi> <mml:mi>t</mml:mi> <mml:mi>i</mml:mi> <mml:mi>c</mml:mi></mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:mn>33</mml:mn> <mml:mspace></mml:mspace> <mml:mi>V</mml:mi></mml:mrow> <mml:annotation>${{\eta }_{kinetic}=0.33\ V}$</mml:annotation> </mml:semantics> </mml:math> .