Electrochemical production of H2O2 is a cost-effective and environmentally friendly alternative to the anthraquinone-based processes. Metal-doped carbon-based catalysts are commonly used for 2-electron oxygen reduction reaction (2e–ORR) due to their high selectivity. However, the exact roles of metals and carbon defects on ORR catalysts for H2O2 production remain unclear. Herein, by varying the Co loading in the pyrolysis precursor, a Co–N/O-C catalyst with Faradaic efficiency greater than 90% in alkaline electrolyte was obtained. Detailed studies revealed that the active sites in the Co–N/O-C catalysts for 2e–ORR were carbon atoms in C–O–C groups at defect sites. The direct contribution of cobalt single atom sites and metallic Co for the 2e–ORR performance was negligible. However, Co plays an important role in the pyrolytic synthesis of a catalyst by catalyzing carbon graphitization, tuning the formation of defects and oxygen functional groups, and controlling O and N concentrations, thereby indirectly enhancing 2e–ORR performance.
In certain metalloenzymes, multimetal centers with appropriate primary/secondary coordination environments allow carbon−carbon coupling reactions to occur efficiently and with high selectivity. This same function is seldom realized in molecular electrocatalysts. Herein we synthesized rod-shaped nanocatalysts with multiple copper centers through the molecular assembly of a triphenylphosphine copper complex (CuPPh). The assembled molecular CuPPh catalyst demonstrated excellent electrochemical CO 2 fixation performance in aqueous solution, yielding high-value C 2+ hydrocarbons (ethene) and oxygenates (ethanol) as the main products. Using density functional theory (DFT) calculations, in situ X-ray absorption spectroscopy (XAS) and quasi-in situ X-ray photoelectron spectroscopy (XPS), and reaction intermediate capture, we established that the excellent catalytic performance originated from the large number of double copper centers in the rod-shaped assemblies. Cu−Cu distances in the absence of CO 2 were as long as 7.9 Å, decreasing substantially after binding CO 2 molecules indicating dynamic and cooperative function. The double copper centers were shown to promote carbon−carbon coupling via a CO 2 transfer-coupling mechanism involving an oxalate (OOC−COO) intermediate, allowing the efficient production of C 2+ products. The assembled CuPPh nanorods showed high activity, excellent stability, and a high Faradaic efficiency (FE) to C 2+ products (65.4%), with performance comparable to state-of-the-art copper oxide-based catalysts. To our knowledge, our findings demonstrate that harnessing metalloenzyme-like properties in molecularly assembled catalysts can greatly improve the selectivity of CO2RR, promoting the rational design of improved CO2 reduction catalysts.
The Cu+/Cu0 interface in the Cu-based electrocatalyst is essential to promote the electrochemical reduction of carbon dioxide (ERCO2) to produce multi-carbon hydrocarbons and alcohols with high selectivity. However, due to the high activity of the Cu+/Cu0 interface, it is easy to be oxidized in the air. How to control and prepare a Cu-based electrocatalyst with an abundant and stable Cu+/Cu0 interface in situ is a huge challenge. Here, combined with density functional theory (DFT) calculations and experimental studies, we found that the trace halide ions adsorbed on Cu2O can slow the reduction kinetics of Cu+ → Cu0, which allowed us to in-situ well control the synthesis of the CuO-derived electrocatalyst with rich Cu+/Cu0 interfaces. Our Cu catalyst with a rich Cu+/Cu0 interface exhibits excellent ERCO2 performance. Under the operation potential of −0.98 V versus RHE, the Faraday efficiency of C2H4 and C2+ products are 55.8 and 75.7%, respectively, which is about 16% higher than that of CuO-derived electrocatalysts that do not use halide ions. The high comes from the improvement of the coupling efficiency of reaction intermediates such as CO–CO, which is proved by DFT calculations, and the suppression of hydrogen evolution reaction. Therefore, we provide an in-situ engineering strategy, which is simple and effective for the design and preparation of high-performance ERCO2 catalysts.
Metal−oxide interfaces on Cu-based catalysts play very important roles in the low-temperature water−gas shift reaction (LT-WGSR). However, developing catalysts with abundant, active, and robust Cu-metal oxide interfaces under LT-WGSR conditions remains challenging. Herein, we report the successful development of an inverse copper−ceria catalyst (Cu@CeO 2 ), which exhibited very high efficiency for the LT-WGSR. At a reaction temperature of 250 °C, the LT-WGSR activity of the Cu@CeO 2 catalyst was about three times higher than that of a pristine Cu catalyst without CeO 2 . Comprehensive quasi-in situ structural characterizations indicated that the Cu@CeO 2 catalyst was rich in CeO 2 /Cu 2 O/Cu tandem interfaces. Reaction kinetics studies and density functional theory (DFT) calculations revealed that the Cu + /Cu 0 interfaces were the active sites for the LT-WGSR, while adjacent CeO 2 nanoparticles play a key role in activating H 2 O and stabilizing the Cu + /Cu 0 interfaces. Our study highlights the role of the CeO 2 /Cu 2 O/Cu tandem interface in regulating catalyst activity and stability, thus contributing to the development of improved Cu-based catalysts for the LT-WGSR.
This study investigates the adsorption and oxidation of isoprene, the most abundant biogenic volatile organic compound, on two common Mn(IV) (hydr)oxides in Earth's surface environment, birnessite and cryptomelane. Both minerals show high adsorption capability toward isoprene under increasing environmental temperature and low relative humidity, whereas the adsorbed isoprene on birnessite is oxidized into carboxylate species, mainly formate. For both Mn(IV) (hydr)oxides, the adsorption of isoprene not only reduces Mn 4+ to Mn 3+ but also gives rise to the slight distortion of the crystal structure. Compared to cryptomelane, birnessite exhibits better adsorption and oxidation capability of isoprene, which is improved by the decrease in crystallinity. This is attributed to the high density of oxygen anions on the (001) surface, owing to the participation of lattice oxygen, electrophilic adsorbed oxygen, and hydroxyl groups in the oxidation of isoprene. For cryptomelane, the particles with short and thick nanorods show higher adsorption capacity but lower oxidizability than those with long and sharp nanorods, as the (001) surface of cryptomelane prefers to adsorb isoprene and Mn 4+ in long sharp nanorods and accept more electrons from isoprene. Based on the experimental results, we propose that Mn(IV) (hydr)oxide in soil dust aerosols is an important regulator of atmospheric isoprene, which enhances the bioavailability of both isoprene and Mn(IV) (hydr)oxides.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.