Highly Selective Electrochemical Reduction of CO2 to Alcohols on an FeP Nanoarray
Lei JiLei LiXuqiang JiYa ZhangShiyong MouTongwei WuQian LiuBaihai LiXiaojuan ZhuYonglan LuoXifeng ShiAbdullah M. AsiriXuping Sun
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Electrochemical reduction of CO2 into various chemicals and fuels provides an attractive pathway for environmental and energy sustainability. It is now shown that a FeP nanoarray on Ti mesh (FeP NA/TM) acts as an efficient 3D catalyst electrode for the CO2 reduction reaction to convert CO2 into alcohols with high selectivity. In 0.5 m KHCO3 , such FeP NA/TM is capable of achieving a high Faradaic efficiency (FE CH3OH ) up to 80.2 %, with a total FE CH3OH+C2H5OH of 94.3 % at -0.20 V vs. reversible hydrogen electrode. Density functional theory calculations reveal that the FeP(211) surface significantly promotes the adsorption and reduction of CO2 toward CH3 OH owing to the synergistic effect of two adjacent Fe atoms, and the potential-determining step is the hydrogenation process of *CO.Keywords:
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The aqueous iron electrode is attractive for large-scale energy storage because of its long life and low materials cost. The redox potential of the Fe ↔ Fe 2+ reaction is approximately 50 mV negative of that of the hydrogen evolution reaction. Hydrogen evolution therefore causes self discharge of the iron electrode during rest and competes with the iron reaction during charge. Here we model the effect of electrode design and cell operation on the coulombic efficiency of charging the iron electrode at modest charging rates (<C/20). Kinetic parameters (exchange current density and transfer coefficients) for the iron dissolution-precipitation reaction and for the hydrogen evolution reaction are estimated from experimental measurements of electrode overpotential and hydrogen generation rate. The volume change from Fe(OH) 2 to Fe metal results in a significant increase in porosity during charge and results in change in electrochemically active surface area. The porous-electrode model includes transport in the electrolyte, Butler-Volmer kinetics, and change in volume and surface area. The model provides a theoretical explanation for experimental observations that coulombic efficiency decreases with decreasing charge rate, and that coulombic efficiency is lower in thicker electrodes. We then use the model to explore the impact for large-format cells of electrode size and design on coulombic efficiency.
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Abstract Electroreduction of CO 2 to HCOO − can be considered as the most economically valuable process. Herein, we developed lysine‐functionalized SnO 2 nanoparticles (SnO 2 ‐lys) as an efficient catalyst for the electroreduction of CO 2 into HCOO − . During CO 2 electroreduction, SnO 2 ‐lys achieved a Faradaic efficiency for HCOO − of higher than 80% over a wide range of applied potentials from −0.5 V to −2.3 V versus reversible hydrogen electrode ( vs . RHE). Notably, the partial current density for HCOO − reached as high as −351.9 mA cm −2 at −2.3 V vs . RHE. On account of kinetic analysis and mechanistic study, lysine‐functionalized SnO 2 facilitated faradaic process and accelerated reaction kinetics via enhancing the CO 2 activation, thus promoting the catalytic performance of the electroreduction of CO 2 into HCOO − .
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Developing a highly active and cost-effective cathode electrocatalyst with strong stability for oxygen reduction reaction (ORR) is extremely necessary. In this work, we reported a facile synthetic path to prepare a hybrid nanostructure formed of nitrogen-doped Ketjenblack carbon (N-KC) supported Co3O4 nanoparticles (Co3O4/N-KC), which could be used as a promising and stable electrocatalyst for ORR. Compared with the physical mixture of Co3O4 and N-KC and pure N-KC samples, the resulting Co3O4/N-KC nanohybrid afforded remarkably superb ORR activity with a half-wave potential of 0.82 V (vs. reversible hydrogen electrode, RHE) and a limiting current density of 5.70 mA cm-2 in KOH solution (0.1 M). Surprisingly, the Co3O4/N-KC sample possessed a similar electrocatalytic activity but better durability to the 20 wt% Pt/C catalyst. The remarkable ORR activity of the Co3O4/N-KC nanohybrid was mainly due to the strong coupling effect between Co3O4 and N-KC, the N species dopant, high electroconductivity, and the large BET surface area. Our work enlightens the exploitation of advanced Co3O4/carbon hybrid material alternative to the Pt-based electrocatalysts.
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Traditionally, ammonia (NH3 ) is synthesized via the Haber-Bosch process, which is not only commanded by harsh conditions but causes serious environmental pollution. Electrochemical reduction is recognized as a mild and environmentally benign alternative approach for NH3 synthesis, but an efficient electrocatalyst is a prerequisite for NH3 production. In this communication, the first experimental demonstration that Mn3 O4 nanocubes can be used as an efficient non-noble-metal electrocatalyst for N2 reduction reaction (NRR) at ambient conditions is reported. In 0.1 m Na2 SO4 aqueous solution, the catalyst delivers excellent NRR activity with an NH3 yield of 11.6 µg h-1 mg-1cat. and Faradaic efficiency of 3.0% at -0.8 V versus reversible hydrogen electrode. Notably, this catalyst also possesses satisfactory durability during the electrolysis and recycling test.
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Previous studies on the electrochemical reduction of CO 2 at metallic electrodes suggest that the adsorption of hydrogen species is structure-sensitive. [1] Surface roughening is likely to introduce defects favorable for the reaction of adsorbed hydrogen atoms, an important intermediate step in the electro-reduction of CO 2 in protic media. [1, 2] Furthermore, roughened surfaces have been shown to be more selective toward hydrocarbon products, which was attributed to a higher number of uncoordinated metal sites. [2] These finding were confirmed by DFT calculations, which suggest that CO 2 activation and reduction occurs at these sites. [3] To further gauge the effect of morphology on the faradaic efficiency and distribution of products obtained during the electroreduction of CO 2 , Cu and Sn foams were electrosynthesized on Cu substrates using a recently reported process. [4] The metal foams were found to be mechanically stable during their preparation, handling, and use in the electrocatalytic reduction of CO 2 . Both Cu and Sn foams are attractive metals for the electrocatalytic reduction of CO 2 because of their low cost and non-toxic nature. Electroreduction of CO 2 was performed in a typical H-cell under potentiostatic conditions. The faradaic efficiency of producing formate from CO 2 at the metal foams and the equivalent planar metal electrode are compared in Figure 1a and 1b. The faradaic efficiencies obtained with the Cu foam electrode were found to be higher at all potentials with a maximum efficiency of 37% at -1.5V for HCOOH. Previously reported data is included for comparison. [5] Likewise, the faradaic efficiencies for HCOOH generation at the Sn foam electrode were found to be higher at all potentials with a maximum efficiency of 89.5% at -1.7V. Previously reported data with slightly different conditions (Sn gas diffusion cell in 0.5 M NaHCO 3 ) is included for comparison. [6] XRD analysis of the Cu and Sn foams did not reveal major differences in the relative ratio of dominant crystal facets when compared to the equivalent planar samples of high purity metal. The hierarchical nature of the pore architecture along with high surface area of the metal foams could affect the reaction kinetics and contribute to the observed increase in faradaic efficiency. For example, the porous nature of the metal foams may promote interactions between incoming CO 2 , adsorbed surface species, electrolyte, and reducing equivalents that are novel relative to the same reaction at a planar electrode. The effect of varying the electrodeposition time and resulting foam architecture on the electroreduction of CO 2 will be the focus of this presentation. References Hori, Y., A. Murata, and R. Takahashi, Formation of hydrocarbons in the electrochemical reduction of carbon dioxide at a copper electrode in aqueous solution. Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases, 1989. 85 (8): p. 2309-2326. Tang, W., A.A. Peterson, A.S. Varela, Z.P. Jovanov, L. Bech, W.J. Durand, S. Dahl, J.K. Norskov, and I. Chorkendorff, The importance of surface morphology in controlling the selectivity of polycrystalline copper for CO2 electroreduction. Physical Chemistry Chemical Physics, 2012. 14 (1): p. 76-81. Durand, W.J., A.A. Peterson, F. Studt, F. Abild-Pedersen, and J.K. Nørskov, Structure effects on the energetics of the electrochemical reduction of CO2 by copper surfaces. Surface Science, 2011. 605 (15–16): p. 1354-1359. Shin, H.C., J. Dong, and M. Liu, Nanoporous Structures Prepared by an Electrochemical Deposition Process. Advanced Materials, 2003. 15 (19): p. 1610-1614. Kuhl, K.P., E.R. Cave, D.N. Abram, and T.F. Jaramillo, New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces. Energy & Environmental Science, 2012. 5 (5): p. 7050-7059. G.K.S. Prakash, F.A. Viva, G.A. Olah, Electrochemical reduction of CO2 over Sn-Nafion® coated electrode for a fuel-cell-like device , Journal of Power Sources, 223 (2013) 68-73.
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