Activity For Reduction Of CO Research Articles

One-pot synthesis of Ni(Ⅱ)-doped UiO-66-NH2 for enhanced photocatalytic CO2 reduction to CO with efficient charge transfer

Introducing a new metal into the metal center of metal–organic framework materials (MOFs) to alter their original electron transfer pathway to improve photocatalytic performance is a promising approach at present. Here, we report a one-pot method to introduce Ni2+ into the metal-centered Zr-O clusters of UiO-66-NH2 (UN) to create a series of Ni2+-doped bimetallic materials (xNi-UN). Experimental results showed that the 0.5Ni-UN exhibited the highest photocatalytic CO2 reduction activity, with a CO yield of 9.01 µmol g-1h−1 under visible light irradiation, which was 2.46 times higher than that of UN (3.67 µmol g-1h−1). Through a number of characterization analyses, we find that the doped Ni2+ replaced the part of original metal center Zr4+ to form a bimetallic UiO-66-NH2 (Zr/Ni), which changed the energy band gap of UiO-66-NH2 and improved the charge transfer. More importantly, the introduction of Ni2+ enhanced the efficiency of interfacial charge transfer from the organic ligand (2-aminoterephthalic acid) to the Zr-O cluster, enabling a metal-to-metal charge transfer (MMCT) pathway, which exhibited higher photocatalytic CO2 to CO reduction activity.

In situ preparation of a novel Z-scheme BiOBr/BiVO4 composite film with enhanced photocatalytic CO2 reduction performance

A kind of novel BiOBr/BiVO4 Z-scheme heterojunction composite film is in situ synthesized on Bi substrates via the electrochemical ion-exchange method, and the composite film exhibits excellent photocatalytic CO2 to CO reduction activity.

Pulsed Electrochemical CO Reduction on Mass-Selected Cu Nanoparticles

Up to date copper is the only electrocatalyst with relevant activity for the reduction of CO2 and CO to value added hydrocarbons and alcohols1. However, CO reduction studies over nanostructured copper catalysts, which are believed to have a high abundancy of active sites, were hindered by coppers instability in alkaline conditions. This instability makes Cu-based catalysts prone to dissolution during immersion into the electrolyte. Recently, we reported on an experimental methodology for immersing catalysts under potential control in reactors generally used for CO2 and CO reduction2. Compared to experiments without electrocatalyst immersion under potential control our method increases the CO reduction activity by four orders of magnitude, showing that small, mass-selected Cu nanoparticles are active catalysts for electrochemical CO reduction. This improvement in activity is attributed to the inhibition of Cu dissolution during immersion into the electrolyte as demonstrated by subsequent Cu stripping experiments.We now utilize the above described methodology to study the pulsed electrochemical CO reduction on 5.2 nm mass-selected Cu nanoparticles. Pulsed electrolysis has shown promise to improve CO(2) reduction activity and steer product selectivity by potential oscillations3–5. Nevertheless, detailed mechanistic understanding of the dynamic reactivity upon potential pulsing is still lacking. Using highly sensitive electrochemical mass-spectrometry we demonstrate a highly active transient activity over mass-selected Cu nanoparticles. By conducting pulsed electrolysis in different electrolytes we ascribe the high transient activity to an initial presence and local depletion of proton donors. Our results highlight the importance of proton donor nature and its local concentration to guide activity and selectivity. We believe that similar strategies can be of importance for the selective conversion of more complex biomass molecules and electrosynthesis.References(1) Nitopi, S.; Bertheussen, E.; Scott, S. B.; Liu, X.; Engstfeld, A. K.; Horch, S.; Seger, B.; Stephens, I. E. L.; Chan, K.; Hahn, C.; Nørskov, J. K.; Jaramillo, T. F.; Chorkendorff, I. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Chemical reviews 2019, 119 (12), 7610–7672. DOI: 10.1021/acs.chemrev.8b00705. Published Online: May. 22, 2019.(2) Hochfilzer, D.; Sørensen, J. E.; Clark, E. L.; Scott, S. B.; Chorkendorff, I.; Kibsgaard, J. The Importance of Potential Control for Accurate Studies of Electrochemical CO Reduction. ACS Energy Lett. 2021, 6 (5), 1879–1885. DOI: 10.1021/acsenergylett.1c00496.(3) Kimura, K. W.; Fritz, K. E.; Kim, J.; Suntivich, J.; Abruña, H. D.; Hanrath, T. Controlled Selectivity of CO2 Reduction on Copper by Pulsing the Electrochemical Potential. ChemSusChem 2018, 11 (11), 1781–1786. DOI: 10.1002/cssc.201800318. Published Online: May. 22, 2018.(4) Bui, J. C.; Kim, C.; Weber, A. Z.; Bell, A. T. Dynamic Boundary Layer Simulation of Pulsed CO 2 Electrolysis on a Copper Catalyst. ACS Energy Lett. 2021, 1181–1188. DOI: 10.1021/acsenergylett.1c00364.(5) Arán-Ais, R. M.; Scholten, F.; Kunze, S.; Rizo, R.; Roldan Cuenya, B. The role of in situ generated morphological motifs and Cu(i) species in C2+ product selectivity during CO2 pulsed electroreduction. Nat Energy 2020, 5 (4), 317–325. DOI: 10.1038/s41560-020-0594-9.

Operando Spectroscopic Investigations of Copper and Oxide-Derived Copper Catalysts for Electrochemical CO Reduction

Oxide-derived copper (OD-Cu) has been shown to favor C2 and C3 products in electrochemical CO reduction at lower overpotentials than polycrystalline copper (Cu-poly). Despite numerous studies and proposed mechanisms, the exact nature of the active phase is still a topic of discussion. In this work, we employ operando attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) to investigate different sites available on Cu-poly and OD-Cu surfaces using CO as a probe molecule. We identify a CO adsorption band on OD-Cu at 2058 cm–1 that is different from those on Cu-poly but resembles CO bound to the Cu(100) facet. In accordance with reactivity studies, we propose that this band corresponding to distinct CO binding sites is responsible for OD-Cu’s enhanced CO reduction activity.

Low-Overpotential Electroreduction of Carbon Monoxide Using Copper Nanowires

We report on Cu nanowires as highly active and selective catalysts for electroreduction of CO at low overpotentials. The Cu nanowires were synthesized by reducing pregrown CuO nanowires, with the surface structures tailored by tuning the reduction conditions for improved catalytic performance. The optimized Cu nanowires achieved 65% faradaic efficiency (FE) for CO reduction and 50% FE toward production of ethanol at potentials more positive than −0.5 V (versus reversible hydrogen electrode, RHE). Structural analyses and computational simulations suggest that the CO reduction activity may be associated with the coordinately unsaturated (110) surface sites on the Cu nanowires.

A Direct Grain-Boundary-Activity Correlation for CO Electroreduction on Cu Nanoparticles.

Copper catalyzes the electrochemical reduction of CO to valuable C2+ products including ethanol, acetate, propanol, and ethylene. These reactions could be very useful for converting renewable energy into fuels and chemicals, but conventional Cu electrodes are energetically inefficient and have poor selectivity for CO vs H2O reduction. Efforts to design improved catalysts have been impeded by the lack of experimentally validated, quantitative structure–activity relationships. Here we show that CO reduction activity is directly correlated to the density of grain boundaries (GBs) in Cu nanoparticles (NPs). We prepared electrodes of Cu NPs on carbon nanotubes (Cu/CNT) with different average GB densities quantified by transmission electron microscopy. At potentials ranging from −0.3 V to −0.5 V vs the reversible hydrogen electrode, the specific activity for CO reduction to ethanol and acetate was linearly proportional to the fraction of NP surfaces comprised of GB surface terminations. Our results provide a design principle for CO reduction to ethanol and acetate on Cu. GB-rich Cu/CNT electrodes are the first NP catalysts with significant CO reduction activity at moderate overpotential, reaching a mass activity of up to ∼1.5 A per gram of Cu and a Faradaic efficiency >70% at −0.3 V.