Amine‐Functionalized Carbon Nanodot Electrocatalysts Converting Carbon Dioxide to Methane

Abstract

The electrochemical conversion of carbon dioxide (CO2) to methane (CH4), which can be used not only as fuel but also as a hydrogen carrier, has drawn great attention for use in supporting carbon capture and utilization. The design of active and selective electrocatalysts with exceptional CO2‐to‐CH4 conversion efficiency is highly desirable; however, it remains a challenge. Here a molecular tuning strategy−in situ amine functionalization of nitrogen‐doped graphene quantum dots (GQDs) for highly efficient CO2‐to‐CH4 conversion is presented. Amine functionalized nitrogen‐doped GQDs achieve a CH4 Faradic efficiency (FE) of 63% and 46%, respectively, at CH4 partial current densities of 170 and 258 mA cm−2, approximating to or even outperforming state‐of‐the‐art Cu‐based electrocatalysts. These GQDs also convert CO2 to C2 products mainly including C2H4 and C2H5OH with a maximum FE of ≈10%. A systematic analysis reveals that the CH4 yield varies linearly with amine group content, whereas the C2 production rate is positively dependent on pyridinic N dopant content. This work provides insight into the rational design of carbon catalysts with CO2‐to‐CH4 conversion efficiency at the industrially relevant level.

Applications of Carbon Dots for the Photocatalytic and Electrocatalytic Reduction of CO2

“…Such a boosting effect was found to be even more pronounced for GQDs enriched with NH 2 functionalities, leading to maximum FE and partial current density of 70.0% and −200 mA cm −2 for CH 4 production, respectively [ 100 ]. In agreement with these findings, an in situ amine functionalization strategy of N-CDs which ensured a better control over the total and the specific N active sites incorporated into the carbon nanostructure, led to a significant improvement of the CO 2 -to-CH 4 performances [ 90 ]. The total N atomic content in the N-GQDs was found to positively impact the overall CO 2 RR performances, whereas the catalytic selectivity was dependent on the specific type of N configurations.…”

“…However, the most conventional sources are commercial precursors, such as citric acid [ 68 , 69 , 70 , 71 , 72 , 73 , 74 ], glucose [ 75 , 76 , 77 , 78 ], ascorbic acid [ 79 , 80 ], polyethylene glycol [ 81 , 82 ], and ethylene glycol [ 83 ]. Other heteroatom-containing precursors, such as urea [ 68 , 84 , 85 , 86 , 87 , 88 , 89 , 90 ] chitosan [ 91 , 92 , 93 , 94 ], ethylenediamine [ 37 , 71 , 73 , 77 , 95 ], thiourea [ 72 , 96 ], cysteine [ 74 ], cetrimonium bromide (CTAB) [ 97 ], phenylenediamine [ 98 ], ammonium citrate [ 99 ], and nitropyrene [ 100 , 101 ] are used to dope the CDs with Nitrogen and/or Sulphur (N-CDs, S-CDs and N,S-CDs). N-doping can also originate from thermal treatment of the carbon precursor in N-containing solvents such as acetonitrile [ 90 ].…”

“…The total N atomic content in the N-GQDs was found to positively impact the overall CO 2 RR performances, whereas the catalytic selectivity was dependent on the specific type of N configurations. The FE and production rate for CH 4 and C 2 products displayed a linear correlation with the content of –NH 2 and pyridinic N dopants, respectively, whereas any specific relationships with CO 2 RR selectivity toward a certain product were obtained for pyrrolic N, graphitic N, and nitrogen oxide functionalities [ 90 ].…”

Recent development of nanomaterials for carbon dioxide electroreduction

“…They could be divided into metal‐based QDs, such as Pb/Au/Ag/Cu vacancy‐rich QD‐derived catalysts (QDDCs), 13 Sn QDs, 14 InP colloidal quantum dots (CQDs), 15 and metal‐free‐based QD, such as GQDs or other carbon nanodots 16 . GQD has been shown to exhibit copper‐like activity to reduce CO 2 into high‐order hydrocarbon 17–20 . GQDs refer to the carbon in a honeycomb structure with a size <100 nm 21,22 .…”

“…16 GQD has been shown to exhibit copper-like activity to reduce CO 2 into high-order hydrocarbon. [17][18][19][20] GQDs refer to the carbon in a honeycomb structure with a size <100 nm. 21,22 Compared to graphene, GQDs have much higher edge-abundance and defects, which exhibit different physical and chemical properties.…”