The electrocatalytic reduction of CO2 (CO2RR) and H+ (or H2O) into chemicals and fuels is attracting attention as a way to address current energy and environmental issues. One of the main focus in this field is the development and understanding of electrocatalysts that can promote the electrochemical CO2 reduction efficiently, and with high selectivity for the desired product. Copper electrodes are extensively studied and stand out because of their unique ability to produce a range of different products including hydrocarbons and oxygenates, which is ascribed to their intermediate binding strength for the CO intermediate. The use of oxide-derived Cu electrodes has arisen, because it promotes CO and COOH formation at low overpotentials, even though the electrodes are operating at potentials where the CuO should be reduced to metallic copper. Inspired by this, some recent studies have also shown that the use of sulfur-containing Cu or sulfide-derived Cu increases the selectivity towards formates, ethanol, propanol, or ethylene at intermediate overpotentials. The origin of these effects is still under debate, but it is often attributed to a change in the binding energy of the intermediates such as *OCHO, *COOH, and CO due to the formation of specific Cu surface structures or the presence of sub-surface sulfur or oxygen in the Cu or mixed phases. In this work, we investigated the phase stability and catalytic performance of carbon-supported sulfide (CuS and Cu2S) derived Cu nanoparticles in the electrochemical reduction of CO2 in aqueous media. The CuS@C and Cu2S@C nanoparticles were prepared via a novel, liquid phase sulfidation method, in which carbon-supported CuO (CuO@C) nanoparticles were converted to either CuS@C (25±13 nm) or Cu2S@C (17±1 nm) as shown in Figure 1a. The stability of the supported nanoparticles was investigated using cyclic voltammetry, where reduction peaks were observed in the first cathodic scans of both CuS@C and Cu2S@C (figure 1c). The reduction was monitored operando under CO2 reduction conditions using in-situ X-ray absorption spectroscopy (XAS). The in-situ XAS spectra showed that at a potential of -0.9V vs. the reversible hydrogen electrode (RHE), both CuS@C and Cu2S@C are reduced to metallic Cu@C. Finally, the products formed by the CuS@C and Cu2S@C-derived catalysts were compared to those of CuO@C-derived catalyst. At current densities of -1.5mA/cm2, the CuS@C- and Cu2S@C-derived catalysts show increased production of formate (figure 1d), while CO production is suppressed, in comparison to the CuO@C catalyst. Cu-sulfide derived catalyst showed differences in formate production, indicating the initial Cu-sulfide phase influences the product selectivity. Figure 1