(66e) Towards an Atomistic Understanding of the Dissolution of Rutile Oxides in Electrocatalytic Water-Splitting
AIChE Annual Meeting
Monday, November 8, 2021 - 9:12am to 9:30am
The oxygen evolution reaction (OER) serves as the bottleneck in the production of hydrogen through electrocatalytic water-splitting owing to its sluggish kinetics. Rutile oxides, especially those of Ru and Ir remain some of the most active materials for the OER but pose the issue of poor stability owing to their dissolution and degradation under operating conditions. Therefore, understanding the stability of these materials under operating conditions is of paramount importance to enable the long-term operation of electrolyzers. Using a combination of first-principles methods involving density functional theory (DFT), ab-initio thermodynamics and ab-initio steered molecular dynamics (AISMD) coupled with enhanced sampling methods, we investigate the surface stability and dissolution of the (110) facet of three prominent electro-(photo-) catalysts; rutile-IrO2, RuO2 and TiO2. From the ab-initio thermodynamics framework, we find that defective surfaces involving Ir and Ru defects are thermodynamically the most stable for both IrO2 and RuO2 (110), while the defect-free surface is largely stable for TiO2 (110) under OER operating conditions, establishing the well-known stability of TiO2. Using the AISMD and enhanced sampling setup in the presence of an explicit solvent, we identify the formation of experimentally observed dissolution intermediates and products for RuO2 and IrO2, establishing possible dissolution paths for the different oxides. We find that there is a distinct surface site-specificity in the dissolution of the different surface sites from the RuO2 (110) surface, while no such site-specificity exists for the IrO2 (110) surface, marking an important distinction in the dissolution mechanism between the two oxides. Additionally, we find that co-dissolution of different surface sites from the RuO2 (110) surface results in a hitherto unreported suppression of the dissolution of Ru from the bridge sites. This provides atomistic features of the dissolution process and paths to resolving the so-called activity-stability conundrum in the design of electrocatalysts for water-splitting.