Electroreduction of carbon dioxide into higher-energy liquid fuels and chemicals is a promising but challenging renewable energy conversion technology. Among the electrocatalysts screened so far for carbon dioxide reduction, which includes metals, alloys, organometallics, layered materials and carbon nanostructures, only copper exhibits selectivity towards formation of hydrocarbons and multi-carbon oxygenates at fairly high efficiencies, whereas most others favour production of carbon monoxide or formate. Here we report that nanometre-size N-doped graphene quantum dots (NGQDs) catalyse the electrochemical reduction of carbon dioxide into multi-carbon hydrocarbons and oxygenates at high Faradaic efficiencies, high current densities and low overpotentials. The NGQDs show a high total Faradaic efficiency of carbon dioxide reduction of up to 90%, with selectivity for ethylene and ethanol conversions reaching 45%. The C2 and C3 product distribution and production rate for NGQD-catalysed carbon dioxide reduction is comparable to those obtained with copper nanoparticle-based electrocatalysts.

Carbon quantum dots (CQDs) have been intensively investigated due to their interesting electrochemical and photoluminescent properties. Here, we report a novel method for large-scale preparation of heavy doped CQDs with tunable photoluminescence. In the present synthetic process, the carbon nanoparticles from Chinese ink were oxidized and cut simultaneously using a mature process to obtain oxidized-CQDs as precursors, and then the heteroatom (N, S or Se) doped CQDs were obtained by a one-step hydrothermal reduction and in situ doping treatment. The heavy doped CQDs are just 1–6 nm size, and have improved photoluminescence with different emission wavelengths, higher quantum yield, longer lifetime and good photostability. Further experiments suggested that these N and S doped CQDs were very sensitive for the detection of Cu²⁺ and Hg²⁺, respectively.