Optimized Platinum Electrocatalyst Designs for Efficient Oxygen Reduction

Reducing the Platinum loading, which is required for the oxygen reduction reaction (ORR), constitutes a huge obstacle toward economically viable commercialization of polymer electrolyte membrane fuel cells (PEMFCs). Tailored pure Pt nanostructured electrocatalysts harbor great potential to enhance the ORR activity, while keeping the high stability of state-of-the-art Pt/C commercial electrocatalysts. Following the Sabatier principle, it is widely accepted that the ORR activity is decisively controlled by the adsorption energies of the reaction intermediates. Weakening the *OH adsorption energy by ~0.1-0.15 eV with respect to Pt(111) improves the ORR activity, which has been shown by various experimental and theoretical studies. Exposing that adsorption energies of ORR intermediates can be fine-tuned in unstrained pure Pt nanostructured electrocatalysts, Calle-Vallejo et al. have extended the geometrical concept of coordination numbers to second nearest neighbors. The generalized coordination number (GCN) reveals fundamental design principles on how to tailor active single sites in pure Pt electrocatalysts. The large effects from atom coordination highlight that the interplay between shapes and sizes tunes the adsorption energies and, therefore, shapes and sizes rule the ORR activity. In our present work, we combine site-specific design principles from theory with experimental studies to develop a computational model, which rapidly predicts ORR mass activities of nanostructured pure Pt electrocatalysts in precise agreement with experiments. Rapid prediction of mass activity is highly essential to identify optimal Pt nanostructures for efficient oxygen electroreduction. Herein, we identify not only optimal nanoparticle sizes, but also shapes, for the oxygen electroreduction on PEMFCs with respect to high mass activity, controllable size distribution, and appropriate mechanical stability. Various kinds of symmetric shapes are created mathematically by a continuously spanned parameter space. The Pt nanostructures are carefully optimized in shape and size toward highest mass activity by Particle Swarm Optimization. Theoretical single-atom-resolved size effect studies, which are performed for the most promising nanostructures, provide chemical routes for experimental synthesis. Our computational screening of thousands of shapes and sizes predicts tailored Pt electrocatalyst shapes with high mass activities up to 4.28 A/mgPt, which corresponds to an enhancement of 780% over Tanaka commercial Pt/C electrocatalysts.      «

Reducing the Platinum loading, which is required for the oxygen reduction reaction (ORR), constitutes a huge obstacle toward economically viable commercialization of polymer electrolyte membrane fuel cells (PEMFCs). Tailored pure Pt nanostructured electrocatalysts harbor great potential to enhance the ORR activity, while keeping the high stability of state-of-the-art Pt/C commercial electrocatalysts. Following the Sabatier principle, it is widely accepted that the ORR activity is decisively cont...     »