Estimating surface electric fields using reactive formic acid probes and SEM image brightness analysis

[Display omitted] •Electric field enhanced catalytic decomposition of gas-phase formic acid.•Reaction used to estimate applied field strength at catalyst active site.•COMSOL model used to predict field structure across Ni foam catalyst.•Applied field is visualized by electron microscopy differential image brightness. By changing the electrical bias imposed on a Ni catalyst attached to an external circuit, the selectivity of catalytic formic acid decomposition is shown to change—favoring CO2/H2 production under negative bias and CO/H2O production under positive bias. A method for estimating the strength of externally generated surface electric fields by measuring this selectivity change is presented and used to approximate field strengths on the order of 0.20 V/nm. A COMSOL model of the catalyst was created which indicated that the presence of Ni particles increased field strength and uniformity across the catalyst. Comparing this model to SEM imaging of the catalyst verified that the field strengths are highest on the surface of the catalyst particles, pore edges, and microscopic defects. The methods developed herein may be useful to future reaction engineers seeking to incorporate applied electric fields into process designs.