The present electrocatalyst consists of copper and copper sulfide nanoparticles dispersed on graphene nanoflakes (GNFs), a stack of 5-20 highly crystalline graphene layers having typical side lengths of 100 by 100 nm. Plasma-based functionalization is used for adding covalently bonded nitrogen sites on the surface of the GNFs to a level of up to 2 at%. The catalyst nanoparticles are synthesized through wet chemistry, where graphene and a copper sulfate salt are mixed in a solvent and dried prior to pyrolysis under inert atmosphere at 700 degrees C. The amount of copper added to the carbon support is well controlled through this method, and is comprised between 20 and 50 wt%. Tests made towards the electrocatalytic reduction of carbon dioxide show these catalysts generate a faradaic efficiency of up to 42.5% toward liquid products at -0.6 V vs RHE, with a high selectivity for formate. The performance of the catalysts is mostly driven by the amount of the copper sulfide phase rather than the metallic copper content, and competes with similar catalysts found in the literature for a fraction of the metal content. (C) 2019 Elsevier Ltd. All rights reserved.