Minimizing the catalyst amount from 1 to 0.05 mg.cm -2 in a series of electrolysis measurements at -0.6 VRHE led to rising the mass activity to 1220 A.g -1 (at 0.05 mg.cm -2 catalyst loading) while the FE remained relatively constant (45-55%). Conversely, the partial current density at -0.6 VRHE is increased to 753 mA.cm -2 through increasing the catalyst loading to 4 mg.cm -2 (Fig. ). Finally, through an extended chronoamperometric measurement at 0.4 VRHE, the FE for NH3 was maintained over the course of 2.5 days (Fig. ). Post-electrolysis EDX-SEM indicates the partial loss of the Al component (Fig. ), a common feature of Al-containing alloys. In addition, a comparison of the X-ray photoelectron spectroscopy (XPS) signals from all components points to substantial changes in electronic structure (Fig. ), as can be expected for dynamic amorphous catalysts. Notably, the Cu 2p3/2 signal shifts from a single peak at 940.1 eV to three peaks at 938.4 and 935.2 and 932.5 eV. This may signal a phase separation during catalysis. The peaks in the post catalysis spectra are situated close to those of CuF2 (936-937 eV), Cu(OH)2