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.

We present a general approach to produce pristine 2D QDs directly from bulk layered materials in common solvents.

Chlorine dioxide oxidation of cysteine (CSH) is investigated under pseudo-first-order conditions (with excess CSH) in buffered aqueous solutions, p[H+] 2.7-9.5 at 25.0 degrees C. The rates of chlorine dioxide decay are first order in both ClO2 and CSH concentrations and increase rapidly as the pH increases. The proposed mechanism is an electron transfer from CS- to ClO2 (1.03 x 10(8) M(-1) s(-1)) with a subsequent rapid reaction of the CS* radical and a second ClO2 to form a cysteinyl-ClO2 adduct (CSOClO). This highly reactive adduct decays via two pathways. In acidic solutions, it hydrolyzes to give CSO(2)H (sulfinic acid) and HOCl, which in turn rapidly react to form CSO3H (cysteic acid) and Cl-. As the pH increases, the (CSOClO) adduct reacts with CS- by a second pathway to form cystine (CSSC) and chlorite ion (ClO2-). The reaction stoichiometry changes from 6 ClO2:5 CSH at low pH to 2 ClO2:10 CSH at high pH. The ClO2 oxidation of glutathione anion (GS-) is also rapid with a second-order rate constant of 1.40 x 10(8) M(-1) s(-1). The reaction of ClO2 with CSSC is 7 orders of magnitude slower than the corresponding reaction with cysteinyl anion (CS-) at pH 6.7. Chlorite ion reacts with CSH; however, at p[H+] 6.7, the observed rate of this reaction is slower than the ClO2/CSH reaction by 6 orders of magnitude. Chlorite ion oxidizes CSH while being reduced to HOCl, which in turn reacts rapidly with CSH to form Cl-. The reaction products are CSSC and CSO3H with a pH-dependent distribution similar to the ClO2/CSH system.

Since the first exfoliation and identification of graphene in 2004, research on layered ultrathin two-dimensional (2D) nanomaterials has achieved remarkable progress. Realizing the special importance of 2D geometry, we demonstrate that the controlled synthesis of nonlayered nanomaterials in 2D geometry can yield some unique properties that otherwise cannot be achieved in these nonlayered systems. Herein, we report a systematic study involving theoretical and experimental approaches to evaluate the Li-ion storage capability in 2D atomic sheets of nonlayered molybdenum dioxide (MoO). We develop a novel monomer-assisted reduction process to produce high quality 2D sheets of nonlayered MoO. When used as lithium-ion battery (LIB) anodes, these ultrathin 2D-MoO electrodes demonstrate extraordinary reversible capacity, as high as 1516 mAh g after 100 cycles at the current rate of 100 mA g and 489 mAh g after 1050 cycles at 1000 mA g. It is evident that these ultrathin 2D sheets did not follow the normal intercalation-cum-conversion mechanism when used as LIB anodes, which was observed for their bulk analogue. Our ex situ XPS and XRD studies reveal a Li-storage mechanism in these 2D-MoO sheets consisting of an intercalation reaction and the formation of metallic Li phase. In addition, the 2D-MoO based microsupercapacitors exhibit high areal capacitance (63.1 mF cm at 0.1 mA cm), good rate performance (81% retention from 0.1 to 2 mA cm), and superior cycle stability (86% retention after 10,000 cycles). We believe that our work identifies a new pathway to make 2D nanostructures from nonlayered compounds, which results in an extremely enhanced energy storage capability.

The hydrogenation of CO2 into useful chemicals provides an industrial-scale pathway for CO2 recycling. The lack of effective thermochemical catalysts currently precludes this process, since it is challenging to identify structures that can simultaneously exhibit high activity and selectivity for this reaction. Here, we report, for the first time, the use of nitrogen-doped graphene quantum dots (NGQDs) as metal-free catalysts for CO2 hydrogenation. The nitrogen dopants, located at the edge sites, play a key role in inducing thermocatalytic activity in carbon nanostructures. Furthermore, the thermocatalytic activity and selectivity of NGQDs are governed by the doped N configurations and their corresponding defect density. The increase of pydinic N concentration at the edge site of NGQDs leads to lower initial reaction temperature for CO2 reduction and also higher CO2 conversion and selectivity toward CH4 over CO.