An exciting example published in 2018 by Clark et al. utilized a functionalized gold electrode via thiol linkage with a rhenium complex to investigate the interfacial electric fields in CO2 reduction (Figure ). Investigations on the binding site of the catalyst provide insight into the strength and implications of the interfacial electric field. Sum frequency generation spectroscopy (SFG) and IR spectroscopy were employed to monitor the shifts of the carbonyl stretching modes in the adsorbed CO2 on the immobilized electrode. CO stretching frequencies and amplitude strongly depended on the applied potential. The magnitude of the interfacial electric field was calculated to be 10 8 -10 9 V/m based on experimental data. It is essential to see the direct relationship between the applied voltage, which can be manually controlled, and the strength of the interfacial electric field, which is considered to influence catalysis by influencing the binding mode of CO2. Remarkably, the order of magnitude of the electric field strength determined in this work resembles the results determined inside active sites in a biological system that bridges the gap between enzymatic, homogenous, and heterogeneous catalysis. FIGURE 26. Study the electric field on the electrode surface modified with a Re complex (SFG, sum frequency generation spectroscopy). Reproduced with permission from Ref. 75. Copyright 2018 American Chemical Society.