The oxygen evolution reaction (OER) is the anodic process associated with electrochemical CO2 reduction, H2 evolution, and NH3 synthesis. However, high overpotentials and costly state-of-the-art catalysts introduce substantial cost-barriers to large-scale deployment of electrochemical systems. Nickel, cobalt, iron, and bimetallic CoFe and NiFe electrocatalysts have shown impressive OER activity, but atomic-level understanding of how catalyst shape, size, and support impact activity are largely lacking in the literature. Here, we present an approach that couples surface science, electrochemistry, and density functional theory (DFT) calculations to synthesize, characterize, and evaluate well-defined transition metal electrocatalysts. We demonstrate this technique with well-defined, ultra-thin Fe2O3 nanocatalysts grown on Au(111) substrates. The two-layer thick (0.6 nm) Fe2O3 nanostructures were systematically varied between discrete nanoparticles and near monolayer coverages to study morphology-dependent OER activity, with maximum activity that exceeded state-of-the-art IrO2. High-resolution scanning tunneling microscopy (STM) imaging quantified the nanocatalyst morphology, and we identified a clear relationship between OER activity and density of edge sites. Complementary DFT calculations confirmed enhanced reactivity at edge sites along the Fe2O3/Au(111) interface with reduced overpotentials and optimization of the ΔGO-ΔGOH activity descriptor. This represents one of the most clearly quantified correlations between electrocatalyst nanostructure and overall activity, and the results confirm long-held hypothesis that undercoordinated edge sites are responsible for catalytic activity. In practical terms, edge sites at the Fe2O3/Au interface promoted OER better than surface sites. We used this insight to create a heterogeneous analog for testing in a full alkaline electrolyzer device. This system produced a maximum geometric current density of 165 mA/cm2geo and showed stable long-term performance during a 16-hour electrolysis. Future efforts will be directed towards more complex bimetallic OER systems to probe how catalyst structure, composition, and active site location impact electrocatalytic activity.

Coupling surface science, electrochemistry, and computation to quantify electrocatalytic structure-property relationships

2019 Spring National Meeting

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