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Sn-decorated Cu (Cu-Sn) electrodes were proposed as an alternative to Ag-and Au-based electrocatalysts for the selective reduction of CO 2 to CO. Here we demonstrate that selectivity does not only depend on catalyst surface composition, but is strongly affected by the electrode morphology. At current densities above 10 mA•cm -2 , we find that morphology can control the CO 2 reduction pathways to CO and other products, including the competing H 2 evolution, on the Cu-Sn surface. An electrode design with dendritic morphological features yields the highest CO partial current density of 11.5 mA•cm -2 at -1.1 V vs. RHE, avoiding the significant loss of CO selectivity observed for an electrode with less sharp, rounder morphological features. Efficient CO 2 mass transport to the catalyst surface and a high local CO 2 concentration, promoted by the dendritic structure, stabilize the Cu-SnO overlayer, suppress the competing H 2 evolution reaction, and maintain CO selectivity above 85% over a wide potential range.

Hydrogen produced by water electrolysis with renewable electricity is a reliable, affordable and environmental friendly energy carrier for future energy supply and storage. Alkaline water electrolysis is a well matured technique and proved to be suitable for large-scale applications. Materials development for alkaline water electrolyzers is still of interest for academia and industry to address the issues of low compatibility to renewable power sources. A lab-scale system for alkaline water electrolysis was developed, aiming to advance materials development and to bridge the intrinsic properties of materials with their performance under realistic operating conditions. As the smallest pressure-type electrolyzer, it is capable of working at 30 bar and 80 °C with continuous liquid electrolyte circulation. Experimental studies investigate the influence of temperature, pressure, and intrinsic properties of materials on voltage efficiency and hydrogen purity. With appropriate analysis, links between material specifications and overall performance can be established, encouraging new designs and material innovations for alkaline water electrolysis.

CO partial current densities of 144 [6g] and 147 mA cm −2 , [7a] respectively.Here, we investigate the electrocatalytic performance and stability of a GDE design for the electrocatalytic reduction of gaseous CO 2 employing earth-abundant tin/copper (Sn/Cu) catalysts. Sn-decorated Cu surfaces were shown previously to provide high selectivity for CO 2 to CO conversion in aqueous electrolyte and achieve CO partial current densities of up to 11.5 mA cm −2 . [8] However, at higher current densities, the hydrogen evolution reaction (HER) starts to dominate due to insufficient CO 2 supply. [8b] To enhance CO 2 mass transport, we develop a process to fabricate electrospun polyvinylidene fluoride (PVDF) nanofibers with uniform Cu coating, and employ electrochemical underpotential deposition (UPD) of Sn to decorate the Cu surface. We demonstrate that Sn/Cu-coated PVDF (Sn/Cu-PVDF) nanofiber GDEs have CO faradaic efficiencies (FEs) above 80%, and achieve high CO partial current densities of up to 104 mA cm −2 , representing the highest reported current density for a Sn/Cu-based catalyst for CO 2 RR to CO.We employ electrospun PVDF nanofiber membranes as templates for fabricating freestanding Cu-nanofiber electrodes (Figure 1; Figure S1, Supporting Information). The PVDF surface is activated by grafting a self-assembled polydopamine (pDA) layer. [9] The pDA layer provides nuclei for electroless Cu deposition from a precursor consisting of 50 × 10 −3 m Cu(II) ethylenediaminetetraacetate (Cu-EDTA) and 0.1 m borane dimethylamine complex. After a reaction at 35 °C for 2 h, conformally Cu-coated PVDF (Cu-PVDF) nanofibers form a conductive network with a sheet resistivity lower than 2.41 Ω. UPD, providing 2D deposition control, is employed to decorate the Cu-PVDF nanofibers with Sn. Control over the exact amount of Sn is critical to obtain high selectivity for CO 2 RR to CO. [8a,b] On CO-selective Sn/Cu catalysts, the initial intermediate of the CO 2 RR is proposed to bind to the surface via the carbon (*COOH). [8g,10] When the amount of Sn on the Cu surface exceeds the optimal value, CO 2 binds to the surface preferentially via the oxygen forming a bidentate *OCHO intermediate, [8g,10] and behaves similarly to a Sn electrode which is selective for HCOO − . [8c-g,11] To quantify the coverage of deposited Sn by UPD, we make use of a polycrystalline Cu rotating disk electrode with an electrochemical surface area of 0.686 cm 2 . Sn UPD from an Ar-saturated 1 × 10 −3 m SnSO 4 + 0.1 m H 2 SO 4 solution correlates to the reduction peak tailing to Earth-abundant Sn/Cu catalysts are highly selective for the electrocatalytic reduction of CO 2 to CO in aqueous electrolytes. However, CO 2 mass transport limitations, resulting from the low solubility of CO 2 in water, so far limit the CO partial current density for Sn/Cu catalysts to about 10 mA cm −2 . Here, a freestanding gas diffusion electrode design based on Sn-decorated Cu-coated electrospun polyvinylidene fluoride nanofibers is demonstrated. The use of gaseous CO 2 as a feedst...

Gold nanoparticles were prepared by electrochemical deposition on highly oriented pyrolytic graphite (HOPG) and boron-doped, epitaxial 100-oriented diamond layers. Using a potentiostatic double pulse technique, the average particle size was varied in the range from 5 nm to 30 nm in the case of HOPG as a support and between <1 nm and 15 nm on diamond surfaces, while keeping the particle density constant. The distribution of particle sizes was very narrow, with standard deviations of around 20% on HOPG and around 30% on diamond. The electrocatalytic activity towards hydrogen evolution and oxygen reduction of these carbon supported gold nanoparticles in dependence of the particle sizes was investigated using cyclic voltammetry. For oxygen reduction the current density normalized to the gold surface (specific current density) increased for decreasing particle size. In contrast, the specific current density of hydrogen evolution showed no dependence on particle size. For both reactions, no effect of the different carbon supports on electrocatalytic activity was observed.