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From chemRxiv

Lattice oxygen evolution in rutile Ru(1−x)Ni(x)O2 electrocatalysts

Efficient predictive tools for oxygen evolution reaction (OER) activity assessment are vital for rational design of anodes for green hydrogen production. Reaction mechanism prediction represents an important pre-requisite for such catalyst design. Even then, lattice oxygen evolution remains understudied and without reliable prediction methods. We propose a computational screening approach using density functional theory to evaluate the lattice oxygen evolution tendency in candidate surfaces. The method is based on a systematic assessment of the adsorption energies of oxygen evolution intermediates on model active sites with varying local structure. The power of the model is shown on model rutile (110) oriented surfaces of a) RuO2, b) Ru(1−x)Ni(x)O2 and c) Ru(1−x)Ti(x)O2. The model predicts a) no lattice exchange, b) lattice exchange at elevated electrode potentials and c) minor lattice exchange at elevated electrode potentials and high titanium content. While in the case of a) and b) the predictions provide sufficiently accurate agreement with experimental data, c) experimentally deviates from the above prediction by expressing a high tendency to evolve lattice oxygen at high titanium content (x = 0.20). This discrepancy can likely be attributed to the presence of structural defects in the prepared material, which are hard to accurately model with the applied methodology.
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Published on November 20, 2023
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Key points
A theory is used to understand how oxygen leaves or evolves from different metal oxides.
Oxygen can come from the oxide itself, this can make some catalysts better.
Energy needed to bind oxygen changes when replacing a ruthenium atom with a nickel atom.
Placing nickel atoms at certain spots on the oxide weakens oxygen bonds and aids its release.
Different mechanisms investigated for oxygen release involve multiple metals or 'popout' oxygen evolve.
Certain specific points on the oxide, like Ni-Ni or AC2, are efficient but not expected to be filled before reaction.
Oxygen evolution depends on the presence of Ru-Ni bridge sites.
Nickel atoms group together differently based on their concentration.
Presence of nickel increases oxygen evolution, but too much nickel can lower it.
Clusters of titanium can activate oxygen release at high electrode potentials.
A method was developed to predict oxygen evolution in particular oxides, relating structure to activity.
Data suggests max oxygen activity with nickel content between 10%-20%, but no activity with low titanium content.
Lattice oxygen evolution in rutile Ru1−xNixO2 electrocatalysts
Page 1
We developed a density functional theory-based computational approach to evaluate the tendency of lattice oxygen evolution in various catalyst surfaces. Our model predicts different lattice oxygen evolution behaviors in surfaces of RuO2, mixed Ru-Ni oxide, and mixed Ru-Ti oxide, with some discrepancies likely caused by structural defects in the studied materials.
Oxygen Evolving Mechanisms
Page 2
We're explaining the oxygen evolving process via Volmer-Heyrovsky and Volmer-Tafel mechanisms. However, an alternative mechanism involving lattice oxygen shows that oxygen from the catalyst's lattice contributes to the overall oxygen evolution. The participation of lattice oxygen improves the overall oxygen evolving activity of some catalysts, especially in Ni-based perovskites and RuO2 and IrO2 based catalysts.