Operando measurements, those taken under conditions in which the catalyst is functioning (in our case in an aqueous electrolyte and applied bias), are finding increased utility in electrocatalysis. We first utilized XRD to understand how structural transformations of the material were linked with its NO3R catalysis. Integrating a home-built electrochemical cell with an XRD setup (Fig. ), we tracked the appearance or dissolution of any crystalline phase within the Cu3Al2OF10. At open circuit, no crystalline peaks from the amorphous Cu3Al2OF10 catalyst were visible, as expected, but once a negative bias of -0.3 VRHE was applied, peaks corresponding to metallic Cu became apparent (Fig. ). The growth of (111) diffraction peak was tracked as a function of potential and was found to initiate just prior to the onset of NO3R (Fig. ), providing evidence that the spontaneously formed Cu within the Cu3Al2OF10 matrix was the active species involved in the catalytic cycle. We next traced the appearance of Cu as a function of time as we switched the potential from 1.0 VRHE to -0.1 VRHE (Fig. ). Within 5 minutes, the signal of the Cu (111) peak reached its full intensity. However, once the potential was returned to 1.0 VRHE, the Cu signal disappeared again. Interestingly, at no point peaks corresponding to CuO or Cu2O detected, indicating that the Cu nanoparticles, as illustrated in Fig. , likely dissolve again into the amorphous Cu3Al2OF10 matrix.