Electrochemical CO2 reduction (ECR) to value-added chemicals offers a promising approach to mitigate net carbon emission but presents challenges for chemistry because of the high energy barrier originating from CO2 activation or product desorption, as well as the limited fundamental understanding of the reaction mechanism. Herein, a diatomic electrocatalyst with nitrogen-doped porous carbon-anchored homonuclear Fe2N6 sites was precisely prepared for efficiently reducing CO2 to CO. The catalyst achieves CO Faradic efficiency up to 96.0% at −0.6 V (RHE) and a Tafel slope of only 60 mV dec–1, much superior to the single-atom Fe catalyst. Density functional theory calculations reveal that neighboring Fe–Fe centers in the Fe2N6 site facilitate the CO2 activation process via concurrently bonding the C and O atoms of the CO2 molecule. Meanwhile, the reaction barrier of CO desorption on the Fe2N6 site is decreased by the synergy of the dual Fe center, as the distinct CO-adsorbed configuration of the Fe2N6 site is inclined to uptake a second CO2 molecule. This work contributes fundamental understanding of ECR mechanisms and provides deep insights into the rational design of efficient ECR catalysts.
The heterogeneous electro-Fenton (hetero-e-Fenton)-coupled electrocatalytic oxygen reduction reaction (ORR) is regarded as a promising strategy for • OH production by simultaneously driving two-electron ORR toward H 2 O 2 and stepped activating the as-generated H 2 O 2 to • OH. However, the high-efficiency electrogeneration of • OH remains challengeable, as it is difficult to synchronously obtain efficient catalysis of both reaction steps above on one catalytic site. In this work, we propose a dual-atomic-site catalyst (CoFe DAC) to cooperatively catalyze • OH electrogeneration, where the atomically dispersed Co sites are assigned to enhance O 2 reduction to H 2 O 2 intermediates and Fe sites are responsible for activation of the as-generated H 2 O 2 to • OH. The CoFe DAC delivers a higher • OH production rate of 2.4 mmol L −1 min −1 g cat −1 than the single-site catalyst Co-NC (0.8 mmol L −1 min −1 g cat −1) and Fe-NC (1.0 mmol L −1 min −1 g cat −1). Significantly, the CoFe DAC hetero-e-Fenton process is demonstrated to be more energy-efficient for actual coking wastewater treatment with an energy consumption of 19.0 kWh kg −1 COD −1 than other electrochemical technologies that reported values of 29.7∼68.0 kW h kg −1 COD −1 . This study shows the attractive advantages of efficiency and sustainability for • OH electrogeneration, which should have fresh inspiration for the development of new-generation wastewater treatment technology.
Graphene oxide (GO) membranes with nanoconfined interlayer channels theoretically enable anomalous nanofluid transport for ultrahigh filtration performance. However, it is still a significant challenge for current GO laminar membranes to achieve ultrafast water permeation and high ion rejection simultaneously, because of the contradictory effect that exists between the water–membrane hydrogen-bond interaction and the ion–membrane electrostatic interaction. Here, we report a vertically aligned reduced GO (VARGO) membrane and propose an electropolarization strategy for regulating the interfacial hydrogen-bond and electrostatic interactions to concurrently enhance water permeation and ion rejection. The membrane with an electro-assistance of 2.5 V exhibited an ultrahigh water permeance of 684.9 L m −2 h −1 bar −1 , which is 1–2 orders of magnitude higher than those of reported GO-based laminar membranes. Meanwhile, the rejection rate of the membrane for NaCl was as high as 88.7%, outperforming most reported graphene-based membranes (typically 10 to 50%). Molecular dynamics simulations and density-function theory calculations revealed that the electropolarized VARGO nanochannels induced the well-ordered arrangement of nanoconfined water molecules, increasing the water transport efficiency, and thereby resulting in improved water permeation. Moreover, the electropolarization effect enhanced the surface electron density of the VARGO nanochannels and reinforced the interfacial attractive interactions between the cations in water and the oxygen groups and π-electrons on the VARGO surface, strengthening the ion-partitioning and Donnan effect for the electrostatic exclusion of ions. This finding offers an electroregulation strategy for membranes to achieve both high water permeability and high ion rejection performance.
Reduced graphene oxide (rGO) could be theoretically used to construct highly permeable laminar membranes with nearly frictionless nanochannels for water treatment. However, their pristine (sp2 C–C) regions usually restack into impermeable channels as a result of van der Waals interactions, resulting in a much low permeance. In this study, we demonstrate that the restacked regions could be electrochemically expanded to form ultrafast water transport nanochannels by providing a low positive potential (e.g., +1.00 V vs SCE) to the rGO membrane. Experimental investigations indicate that the structural expansion is attributed to the intercalation of water molecules into the restacked regions, driven by hydrogen bond interactions between water molecules and hydroxyl groups that are electrochemically produced on edges of rGO nanosheets. The structural expansion could be promoted by weakening the graphene–OH– interactions through intermittent application of the potential. As a result of more ultrafast water transport nanochannels available, the electrochemically treated rGO membranes could have a permeance 2 orders of magnitude higher than that of the pristine one and ∼3 times higher than that of graphene oxide membranes. Because of their smaller average pore size, the rGO membranes also have a higher ionic/molecular rejection performance than graphene oxide membranes.
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