Metal

Gene

Epitaxy

Transformation (genetics)

Oxygen evolution

Engineering

Chemical physics

Electrochemistry

Metallurgy

Materials science

Layer (electronics)

Density functional theory

Biochemistry

Chemical engineering

Surface (topology)

Electrocatalyst

Physical chemistry

Nanotechnology

Mathematics

Thin film

Computational chemistry

Geometry

Chemistry

Electrode

Surface layer

Electrolyte

Electrolysis

Overpotential

Nature Materials

Structure-activity relationships built on descriptors of bulk and bulk-terminated surfaces are the basis for the rational design of electrocatalysts. However, electrochemically driven surface transformations complicate the identification of such descriptors. Here we demonstrate how the as-prepared surface composition of (001)-terminated LaNiO3 epitaxial thin films dictates the surface transformation and the electrocatalytic activity for the oxygen evolution reaction. Specifically, the Ni termination (in the as-prepared state) is considerably more active than the La termination, with overpotential differences of up to 150 mV. A combined electrochemical, spectroscopic and density-functional theory investigation suggests that this activity trend originates from a thermodynamically stable, disordered NiO2 surface layer that forms during the operation of Ni-terminated surfaces, which is kinetically inaccessible when starting with a La termination. Our work thus demonstrates the tunability of surface transformation pathways by modifying a single atomic layer at the surface and that active surface phases only develop for select as-synthesized surface terminations.

Tuning electrochemically driven surface transformation in atomically flat LaNiO3 thin films for enhanced water electrolysis