Structure-Sensitivity of Nitrate Reduction on Bimetallic Surfaces

Excess nitrate (NO₃^- ) leaching from agricultural runoff poses a significant environmental hazard to the nitrogen cycle and the quality of drinking water. Electrocatalytic reduction of NO₃^- is a sustainable route to utilize renewable electricity as a sustainable solution by converting nitrate into environmentally benign nitrogen gas (N₂) or value-added chemicals like ammonia (NH₃). Despite its overall promising outlook, identifying desired catalyst surface properties to promote both N-O dissociation (favored at strong-binding metals) and N-N/N-H bond formation (favored at relatively weak-binding metals) poses a significant challenge to engineer efficient electrode materials for synthesizing the desired product(s).¹ Bimetallic surfaces with a strong binding metal (Pd, Pt) and a weaker binding metal (Ag, Au, Cu) provide binding sites with varying electronic properties to possibly accelerate both classes of reactions and allow tuning of the product selectivity by optimizing the surface composition and distribution.^2,3

This presentation will use density functional theory (DFT) calculations to develop structure-sensitive scaling relations of key reaction intermediates involved in NO₃RR to NO, N₂, and NH₃ on (111) and (100) facets of Pd, Pt, Cu, Au, and Ag bimetallic surfaces. These scaling relations correlate the adsorbate binding energy to be accurately represented as a function of the binding energy of the metal site (BE_M) with mean absolute errors less than 0.07 eV.⁴ This enables us to derive thermodynamic selectivity towards NO, N₂, and NH₃ as a function of a binding site (BE_M). These scaling relations will be further combined with Brønsted-Evans-Polanyi (BEP) relations to calculate activation energies as a function of computationally inexpensive BE_M. Finally, we plan to incorporate the structure-sensitive scaling relations and modified BEP relations in microkinetic modeling to derive the correlation between turnover frequencies and determine the selectivity of desired products as a function of BE_M. This correlation can be used to predict the structure of more active and selective materials for NO₃RR to NH₃ through inverse design.

References

• Liu, J-X. et al., ACS Catal. 9, 7052-7064 (2019)
• Liu, H. et al., ACS Catal 11, 8431-8442 (2021)
• Chun, H.-J. et al., ACS Catal. 12, 1394-1402. (2022)
• Choksi, T. et al., J. Phys. Chem. Lett. 10, 1852-1859 (2019)