Unable to act as a catalyst in its bare form, graphene doped with foreign material becomes defect rich and is capable of adsorbing the reactive species of OER. N being closest in atomic size surfaced as an early doping candidate followed by B, S, P, F, etc. We performed an liquid pahse activation barrier calculation for each step of OER catalysis in the alkaline medium assisted by N, B, S, and P doped graphene using the Langevin metadynamics method. The active site for adsorption is the C adjacent to nitrogen for N doped graphene and the dopant itself for the rest and was confirmed from the Ow and sheet elements radial distribution function. Most significantly our study is based on the choice of level of theory used for metadynamics simulation. The results from the cost-efficient SCC-DFTB with D3, which has been proven to be a reliable method for enzymatic free energy calculation, are compared with PBE-D3. The free energy surfaces provide the activation barrier for steps 1-4, namely OH* adsorption, O* formation, oxo-oxo bond formation, and molecular O2 desorption. The 1st and 3rd steps are more energy demanding compared to the 2nd and 4th, which involve proton transfer, an observation similar to OER catalysis on the Pt surface. The thermodynamically challenging 3rd step turns out to be the rate determining step (RDS), irrespective of the level of theory and the dopant. Doping S on the graphene enhances catalytic efficiency to extremity with the lowest activation barrier for hydroxo complex formation by altering spin density, is followed by B, P, and N. Conspicuously there is an analogous effect of the doping material addressing the 3.5 Kcal mol-1 difference in the activation barrier for the RDS assisted by the best and worst-performing dopant. Also, a very small deviation in the energy barrier values makes DFTB a comparable and reliable method for costly DFT methods.

Quantitative theoretical assessment of the effect of single doping on the oxygen evolution reaction catalysis by graphene

ACS Spring Meeting 2021

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