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Carbon dioxide electroreduction (CO2ELR) can combine the use of a gaseous waste byproduct (CO2) with electricity from renewable sources to produce low‐carbon fuels and useful chemicals. Recent reports pointed out the superior performance of rough copper polycrystalline catalysts; however, reconstruction that takes place on such surfaces is under investigation. This report highlights the importance of copper surface reconstruction on rough surfaces during CO2ELR. Electrodeposited copper‐based catalysts composed primarily of Cu(111) were examined under CO2ELR conditions, and it was found that they underwent reconstruction towards Cu(200). The main hydrocarbon product of electrodeposited copper‐based catalysts with Cu(200) was CH4. The Cu/Cu catalyst achieved up to 40 % Faradaic efficiency (FE) to CH4 and low H2 efficiency (16 % FE) at −1.07 V versus the reversible hydrogen electrode (RHE), at a current density of −86 mA cm−2. This study provides new insights regarding the correlation of copper crystal orientation and selectivity on rough copper surfaces and the impact of copper reconstruction on the reaction.

We investigated the effect of the electrode geometry on the product selectivity and catalytic activity in CO 2 electroreduction (CO2ELR) for equal-surface-area Cu and Ag electrodes. Three different geometries (wire coil, foil coil, and flag) with relatively smooth surfaces were chosen for this study. The electrode geometry impacts the current density distribution on the electrode and the different current densities create an electric field distribution on the electrode surface. The geometry that causes the higher current density distribution (wire coil) showed higher total current density and lower charge transfer resistance, in comparison with the flag-shaped electrodes for both Cu and Ag. The results showed that the current density distribution changes due to the geometry influence the product selectivity as well. Cu coil electrodes showed higher faradaic efficiency (FE) for C 2 products, in comparison to the Cu flag. Ag coil showed higher FE% for CO, compared to the Ag flag.

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Furfural (FF) is a C5 biomass-derived platform chemical obtained from lignocellulose. It can be converted to an industrial adhesive intermediate, furfuryl alcohol (FA), and a promising biofuel candidate, 2-methyl furan (MF) [1]. Liquid phase catalytic hydrogenation and hydrogenolysis (CH) is a widely used manner for biomass conversion. However, it requires large quantities of externally supplied hydrogen gas with high pressure and high temperature [1]. In contrast to CH, electrochemical hydrogenation and hydrogenolysis (ECH) enables biomass conversion at ambient conditions. Also, atomic hydrogen for ECH can be supplied from the aqueous electrolyte. These advantages led to recent studies of electrochemical biomass conversion [2]. From the previous studies for ECH of FF, FA can be obtained at various pH ranges (0 – 13)[2], while MF can be only produced in low pH (0 – 1) solutions. The highest selectivity (c.a. 80%) of MF was shown at pH 0 and 8oC with a Cu foil electrode[3]. A concurrent reaction during ECH of FF is the hydrogen evolution reaction that undesirably consumes electrons[4], which is in competition with ECH of FF. Moreover, from our previous study, we reported that furanic compounds in acidic electrolytes (pH ≤ 1) participate in homogeneous side reactions, decreasing the mole balance closure[5]. This investigation focuses on the combined effects of reaction conditions, copper electrocatalysts and experimental setup towards selective MF production. This is to improve the conversion of FF, yield of MF and energy efficiency with high mole balance for the selective production of MF in pH 0 solution (0.5 M H2SO4). In order to obtain high yield of MF and avoid homogenous side reactions of MF within the acidic solution, vigorous stirring and N2 gas flowing through the reaction solution was introduced to evaporate volatile MF rapidly. Bare Cu foil and micro-sized Cu electrocatalysts, obtained by electrodeposition, have been used as the electrocatalysts. ECH of FF was run at potentials from - 0.5 to - 0.95 V vs RHE. Vigorous stirring and N2 gas flowing improved the mole balance and MF yield. Micro-sized Cu electrocatalysts showed higher conversion of FF and yield of MF compared to bare Cu. In addition, conversion of FF and yield of MF increased as applied potential increased, while faradaic efficiency for FA and MF production increased as applied potential decreased. [1] Y. Nakagawa, M. Tamura, K. Tomishige, Catalytic reduction of biomass-derived furanic compounds with hydrogen, ACS Catalysis, 3 (2013) 2655-2668. [2] Y. Kwon, K.J.P. Schouten, J.C. van der Waal, E. de Jong, M.T.M. Koper, Electrocatalytic conversion of furanic compounds, ACS Catalysis, 6 (2016) 6704-6717. [3] P. Nilges, U. Schröder, Electrochemistry for biofuel generation: production of furans by electrocatalytic hydrogenation of furfural, Energy & Environmental Science, 6 (2013) 2925-2931. [4] R. Parsons, The rate of electrolytic hydrogen evolution and the heat of adsorption of hydrogen, Transactions of the Faraday Society, 54 (1958) 1053-1063. [5] S. Jung, E.J. Biddinger, Electrocatalytic hydrogenation and hydrogenolysis of furfural and the impact of homogeneous side reactions of furanic compounds in acidic electrolytes, ACS Sustainable Chemistry & Engineering, 4 (2016) 6500-6508.

Carbon dioxide (CO­2) is a known greenhouse gas and as such, it is considered responsible for climate change. It is believed that human activities, like farming, combustion, and industrial processes contribute an excess CO2 flow to the atmosphere that disturbs the natural carbon cycle. Carbon dioxide electroreduction (CO2ELR) can be seen as a sustainable process which utilizes this waste and harmful gas and at the same time stores the excess intermittent electricity from renewables. A key parameter of CO2ELR is the catalyst that influences the activity, product selectivity and stability of the system1. At this point, the obstacles towards the broader use of CO2ELR are related to the performance of the catalyst. Copper (Cu) was found to be the only metal that reduces CO2 to hydrocarbons among a variety of metals1. Recent studies showed that the morphology of the Cu surface influences the selectivity and activity of the products2-4. In particular, morphological parameters like roughness factor, crystal orientation, and particle size have been reported to influence the activity and selectivity of the reduction5-7. We recently reported that Cu undergoes reconstruction under CO2ELR conditions that influence the crystal orientation and the morphology something that added more complexity to understanding the morphology-related parameters that drive the performance8. It is critical to understand and identify the factors behind the product selectivity and catalyst activity improvement since it will allow the optimization of the catalyst design towards the desired products. This work investigates the morphological aspects on rough polycrystalline Cu - roughness factor, particle size, and crystal orientation. An analysis of current distribution on the catalyst surface was also performed. Electrodeposition was selected as the synthesis technique due to its ability to control surface morphology of the catalysts through the manipulation of the potential applied and charge passed. Synthesized catalysts were evaluated in terms of their morphology, faradaic efficiency, and activity. Morphology-related aspects were examined with the use of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and capacitance measurements with cyclic voltammetry. Gaseous product analysis was performed with the use of microGC. The results illustrate a direct relation between particle size, current distribution, and roughness with the product selectivity. In particular, high roughness (7.8 roughness factor) and 300nm particle size were related with ethylene (C2H4) formation, whereas low roughness (1.6 roughness factor) and 3μm size particles were associated with methane (CH4).The current distribution analysis showed higher current intensity on high roughness surfaces in comparison with low roughness surfaces under the same potential. 1. Hori, Y., Electrochemical CO2 reduction on metal electrodes. In Modern Aspects of Electrochemistry, Vayenas, C. G.; White, R. E.; Gamboa-Aldeco, M. E., Eds. Springer: New York, 2008; Vol. 42, pp 89-189. 2. Kas, R.; Kortlever, R.; Milbrat, A.; Koper, M. T. M.; Mul, G.; Baltrusaitis, J., Physical Chemistry Chemical Physics 2014, 16 (24), 12194-12201. 3. Tang, W.; Peterson, A. A.; Varela, A. S.; Jovanov, Z. P.; Bech, L.; Durand, W. J.; Dahl, S.; Norskov, J. K.; Chorkendorff, I., Physical Chemistry Chemical Physics 2012, 14 (1), 76-81. 4. Qiao, J.; Jiang, P.; Liu, J.; Zhang, J., Electrochemistry Communications 2014, 38 (0), 8-11. 5. Reske, R.; Mistry, H.; Behafarid, F.; Roldan Cuenya, B.; Strasser, P., Journal of the American Chemical Society 2014, 136 (19), 6978-6986. 6. Mistry, H.; Varela, A. S.; Bonifacio, C. S.; Zegkinoglou, I.; Sinev, I.; Choi, Y.-W.; Kisslinger, K.; Stach, E. A.; Yang, J. C.; Strasser, P.; Cuenya, B. R., Nature Communications 2016, 7, 12123. 7. Takahashi, I.; Koga, O.; Hoshi, N.; Hori, Y., Journal of Electroanalytical Chemistry 2002, 533 (1–2), 135-143. 8. Karaiskakis, A. N.; Biddinger, E. J., Energy Technology 2016, DOI: 10.1002/ente.201600583.

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Carbon dioxide (CO2) electroreduction (CO2ELR) has the advantage of using a gaseous waste stream accompanied with water, a catalyst and electricity from renewables and turn it to carbon neutral chemicals and fuels. The most valuable products of CO2ELR are formed predominantly on Cu-based catalysts, such as methane (CH4), ethylene (C2H4), ethanol, and formic acid. However, there are still hindrances that prevent the broad commercial use of the process and are associated mainly with catalyst performance, such as current efficiency, selectivity, and stability1, 2. Recent studies highlighted the importance of surface morphology which can improve faradaic efficiency (FE) and activity towards more desirable products (hydrocarbons) 3-6. Our recent study showed that Cu undergoes reconstruction under CO2 reduction conditions that influences the surface morphology and the crystal orientation7 which added more complexity to understanding morphology-driven performance. Understanding and identifying the factors behind the activity and selectivity improvement is of great importance since it will allow us to control and direct the reactions towards the targeted products though the optimal design of catalysts. This work examines the morphology-related factors (particle size, roughness, and crystal orientation) and copper oxidation state that drive the selectivity on rough Cu-based catalysts surfaces. Rough Cu-based catalysts were synthesized by electrodeposition and their morphological aspects were tuned through control of the parameters of potential applied and charge passed. A surface current distribution due to morphology was performed for each catalyst. The evaluation of each synthesized catalyst involved the examination of their surface morphology, reaction selectivity, and current efficiency. The surface morphology of each Cu-based catalyst was examined with capacitance measurements using cyclic voltammetry techniques, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM). Micro gas chromatography (microGC) was used for the gaseous product analysis. The results present the factors that influence the selectivity and illustrate a direct relation between specific morphological aspects, current distribution, and product selectivity. In particular, lower roughness catalysts (1.6 roughness factor) covered with larger particles (3μm size particles) produced methane as the main hydrocarbon product; whereas, higher surface roughness catalysts (7.8 roughness factor) covered with smaller particles (300nm size) were associated with the higher formation of ethylene. Current distribution analysis illustrated lower current intensity on low roughness surfaces in comparison with higher roughness surfaces where the current intensity was higher. We will report that the crystal orientation of polycrystalline Cu is not the main factor that drives the selectivity and the oxidized Cu doesn’t seem to enhance the selectivity to C2H4 in comparison with metallic Cu. References 1. Qiao, J.; Liu, Y.; Hong, F.; Zhang, J., Chemical Society Reviews 2014, 43 (2), 631-675. 2. Hori, Y., Electrochemical CO2 reduction on metal electrodes. In Modern Aspects of Electrochemistry, Vayenas, C. G.; White, R. E.; Gamboa-Aldeco, M. E., Eds. Springer: New York, 2008; Vol. 42, pp 89-189. 3. Tang, W.; Peterson, A. A.; Varela, A. S.; Jovanov, Z. P.; Bech, L.; Durand, W. J.; Dahl, S.; Norskov, J. K.; Chorkendorff, I., Physical Chemistry Chemical Physics 2012, 14 (1), 76-81. 4. Qiao, J.; Jiang, P.; Liu, J.; Zhang, J., Electrochemistry Communications 2014, 38 (0), 8-11. 5. Kas, R.; Kortlever, R.; Milbrat, A.; Koper, M. T. M.; Mul, G.; Baltrusaitis, J., Physical Chemistry Chemical Physics 2014, 16 (24), 12194-12201. 6. Reske, R.; Mistry, H.; Behafarid, F.; Roldan Cuenya, B.; Strasser, P., Journal of the American Chemical Society 2014, 136 (19), 6978-6986. 7. Karaiskakis, A. N.; Biddinger, E. J., Energy Technology 2016, DOI: 10.1002/ente.201600583.