Single-particle atomic-scale strain-gradient engineering for high-performance fuel cells

Practical electrochemical energy conversion requires electrocatalysts that coordinate multiple elementary steps at spatially distinct active sites, yet atomic-level control of such site-specific reactivity within a single heterogeneous particle remains challenging. Here we propose and realize atomic-scale gradient strain as a design concept for heterogeneous electrocatalysis. Using Pd@Pt core-shell tetrahedra as a model system, we construct a continuous lattice-strain gradient across individual 3-4 atomic-layer Pt {111} epitaxial shells, where lattice-mismatch-driven compression relaxes from edges to center regions. This single-particle strain gradient, spanning approximately -8% to -2%, spatially links *O₂ activation at highly compressed sites with *OH weakening at moderately compressed sites through kinetically accessible intermediate redistribution. The catalysts exhibit competitive oxygen reduction reaction performance, with mass and specific activities of 2.19 A mg_Pt⁻¹ and 3.01 mA cm⁻² at 0.9 V vs reversible hydrogen electrode, while retaining 91% activity after 20 k cycles. In membrane electrode assemblies, they achieve 0.57 A mg_Pt⁻¹, and peak power densities of 2.10 W cm⁻² in H₂ - O₂ and 1.16 W cm⁻² in H₂-air, with over 90% performance retention after 20 k cycles.