The recovery of gold from wastewater is necessary from both environmental and economic standpoints. Metal-organic frameworks (MOFs) can serve as high-capacity and selective adsorbents, as shown in a recent work by Zhao and co-workers. Their novel three-dimension cationic framework goes further than selectively adsorbing AuCl4- . It also serves as a stable platform to transform adsorbed gold into an efficient catalyst for the electrochemical reduction of CO2 . This work highlights the versatility of MOFs, which can serve as selective adsorbents and as a support for nanoparticle catalysts.

This laboratory experiment consists of the synthesis of two series of alkaline-earth titanates (calcium-strontium and strontium-barium) to corroborate Vegard ' s law by obtaining their X-ray diffraction patterns and plotting the lattice parameter versus mole fraction of both cations. This experiment allows students to understand the key concepts in the solid state chemistry of a lattice parameter, a cubic Bravais network, a perovskite type structure, substitutional solid solutions, Vegard ' s law and its deviations, Miller indices, and X-ray diffraction principles. In addition, it gives students the opportunity to acquire technical skills in ceramic and diffraction

The electrochemical CO2 reduction reaction (CO2RR) is a promising technology for converting waste CO2 into synthetic fuels and carbon-based chemicals using renewable electricity. Most efforts have been dedicated to improving the selectivity at high current densities bringing this process closer to commercial application. However, the long-term stability of the process has received considerably less attention. In this review, we present the progress made on long-term CO2 electrolysis to bring attention to the crucial piece of the puzzle. While Ag-based electrolyzers for CO production have met the desired durability requirements, this is not yet the case for other catalysts. Therefore, we also review the possible degradation pathways affecting both the catalyst material and the electrolyzer and address different strategies to mitigate them.

Contributing to the field: With this Special Collection, the aim is to transcend the barriers of geography and highlight the recent work of Latin American Electrochemists around the world.

The versatility of MOFs is ideal for designing efficient CO2RR electrocatalysts, yet their poor stability and conductivity needs to be improved.

Electrochemical CO2 reduction (CO2R) is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO2R technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application of data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle.

In this issue of Chem Catalysis, Chen et al. report a combined theoretical and experimental study on how the electrolyte and binder affect the CO2 electrochemical reduction reaction (CO2RR). Whereas formate production was independent of the reaction conditions, CO selectivity changed dramatically, which was attributed to bicarbonate’s role as a proton donor for CO formation.

Metal-organic Frameworks (MOFs) have emerged as promising materials for different electrochemical applications. Their low conductivity, however, is a major challenge to overcome. Therefore, a deeper understanding on the charge transfer mechanism is needed to improve the conductivity of MOF-based electrodes. For this contribution, we focused on metalated MOF-525 and found that the nature of the metal center is one of the many factors contributing to the charge transfer kinetics, which is attributed to differences in redox behaviour, affecting the hopping distance and the electron transfer rate. These results highlight the importance of the nature of the redox active site to optimize charge transfer in MOF-based electrodes.

The viability of electrocatalytic CO2 reduction as a pathway for CO2 utilization is contingent on developing selective processes towards high-value carbon-based chemicals. New work demonstrates a strategy to expand the possible products to carbonate esters by sequential redox cycles in a single electrochemical cell.

The direct electrochemical conversion of carbon dioxide (CO2 ) into multi-carbon (C2+ ) products still faces fundamental and technological challenges. While facet-controlled and oxide-derived Cu materials have been touted as promising catalysts, their stability has remained problematic and poorly understood. Herein we uncover changes in the chemical and morphological state of supported and unsupported Cu2 O nanocubes during operation in low-current H-Cells and in high-current gas diffusion electrodes (GDEs) using neutral pH buffer conditions. While unsupported nanocubes achieved a sustained C2+ Faradaic efficiency of around 60 % for 40 h, the dispersion on a carbon support sharply shifted the selectivity pattern towards C1 products. Operando XAS and time-resolved electron microscopy revealed the degradation of the cubic shape and, in the presence of a carbon support, the formation of small Cu-seeds during the surprisingly slow reduction of bulk Cu2 O. The initially (100)-rich facet structure has presumably no controlling role on the catalytic selectivity, whereas the oxide-derived generation of under-coordinated lattice defects, can support the high C2+ product yields.

The CO2 electrochemical reduction reaction (CO2RR) is seen as a promising technology for converting waste CO2 into carbon-based chemicals using renewable electricity to drive the reaction. The technological viability of this process is contingent on reducing CO2 selectively into one product with high current densities. With this purpose, several groups are studding different materials as electrocatalysts to establish relationships between catalyst structure and its performance. Although the catalyst is crucial for the reaction, the reaction conditions such as electrolyte, CO2 pressure, and working potential also play an important role on the catalytic performance which needs to be understood to optimize the process. This work focusses on the effect that the working pH has on the selectivity of the CO2RR and discuss how the process can be optimized by controlling the concentration of protons near the interphase.

We demonstrate the direct electrochemical conversion of CO2 to CO using solid state Ni–N–C carbon catalysts characterized by a coordinative molecular Ni–Nx active moiety at industrial current densities of up to 700 mA cm−2 with faradaic efficiencies superior to those of the state-of-the-art AgOx electrocatalysts.

The need of a sustainable society to advance towards a circular economy, in which there is a balance between the emission and capture of anthropogenic gases like carbon dioxide (CO 2 ), is of utmost scientific and technological importance to ensure the increase or rather preservation of the current prosperity for future generations. The growing global population and increase in worldwide prosperity is tightly connected to a rise in power consumption. Traditionally, this energy demand is supplied by the combustion of fossil fuels, resulting in growing emission of greenhouse gases. In this, CO 2 is a key issue which climatic influences and general mitigation is rigorously disused not only in scientific field, but in politics as well. Here, the electrochemical CO 2 reduction reaction (CO 2 RR) is posing as one potential technology, to address questions of power storage for renewable energies and sustainable usage of natural resources. The CO 2 RR shows a diverse spectrum of products ranging from liquid fuels, as ethanol and propanol, to gaseous building blocks for the chemical industry, as ethylene and CO. The selectivity of this reaction is highly dependent on the nature of the catalyst and is always competing with the hydrogen evolution reaction (HER), due to the aqueous conditions. Recently, very selective and active catalysts have been developed for the production of CO and formic acid. Both compounds are comparably easy to produce, as the reduction only involves the transfer of 2 electrons. Unfortunately, the production of valuable hydrocarbons is much more difficult and suffers from losses in selectivity due to the highly complex reaction mechanism. So far, only copper showed acceptable production rates for hydrocarbons, owing to the favorable binding energies of intermediates. Recent studies have been focused on fundamental parameters to control the selectivity of this complex reaction on copper for C 2+ species, ranging from catalyst design to electrolyte selection. On the catalyst side, many effects as the presence of (100) facets 1 , grain boundaries 2 and oxides 3 have been suggested to be beneficial, whereas influences of buffer capacity and local electric field brought additional advantages by choice of the electrolyte. While promising results were shown, many studies only focused on low-current density, which are far from an industrial application. Here, at least 200 mA cm -2 are needed for a functional electrolyzer. This poses as a discrepancy between research and application and raises the question if the results from fundamental studies can be transferred to full size electrolyzers. 4 For this, we are presenting a cubic Cu 2 O catalyst, which we investigate in a comprehensive study, moving from initial tests in an H-Cell towards high currents on a Gas Diffusion Electrode (GDE) in a Flow-Cell setup. To deconvolute the parameters dictating CO 2 RR selectivity, we used X-Ray-Diffraction (XRD), quasi in-situ X-Ray Photon Spectroscopy (XPS) and operando X-ray Absorption Spectroscopy (XAS) to trace phase changes during reaction, in addition to morphological investigations by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). This complementary analysis depicts a highly dynamic system, in which the reduction of oxidized Cu progresses from the surface towards deeper layers, resulting in a purely metallic, defect-rich material. We further focus on performance tests of our Cu 2 O catalyst at high current density of up to 700 mA cm -2 in a flow-electrolyzer. By varying system parameters as mass loading and nafion content we observe strong changes in selectivity and activity during CO 2 RR, which we correlate to accessibility of the active copper sites and issues of mass transport. We further discuss the role of surface pH at high current density by varying electrolyte concentration and therefore buffer capacity. Our study suggests distinct differences between CO 2 RR in electrochemical cells for fundamental studies at low currents compared to tests at high currents in a flow-electrolyzer. Furthermore, we show how recent results from literature translate to performance at high current density and comment on the importance of electrode preparation. Y. Hori, I. Takahashi, O. Koga and N. Hoshi, Journal of Molecular Catalysis A: Chemical , 2003, 199 , 39-47. A. Verdaguer-Casadevall, C. W. Li, T. P. Johansson, S. B. Scott, J. T. McKeown, M. Kumar, I. E. L. Stephens, M. W. Kanan and I. Chorkendorff, Journal of the American Chemical Society , 2015, 137 , 9808-9811. H. Mistry, A. S. Varela, C. S. Bonifacio, I. Zegkinoglou, I. Sinev, Y.-W. Choi, K. Kisslinger, E. A. Stach, J. C. Yang, P. Strasser and B. R. Cuenya, Nature Communications , 2016, 7 , 12123. T. Burdyny and W. A. Smith, Energy & Environmental Science , 2019, DOI: 10.1039/c8ee03134g.

For CO2 reduction reactions, the Cu catalyst is unique, as compared with other metals, because of its ability to produce a wide range of hydrocarbon and oxygenated products. Previously, we have shown that Cu has the unique property of binding CO* without having H* UPD (underpotential deposited). However, the product distribution from Cu depends highly on the exact nature of the Cu surface. In this work, we investigate a series of Cu facets to understand how they affect the product distribution. Some carbon-carbon (CC)-coupled products are statistically shown to highly correlate, while other CC products correlate with C-1 products. We avoid studying the complex reaction network of the CO2 reduction reaction and focus instead on descriptors for the Cu facet product distribution. The coordination number distribution and the binding energies of the intermediates calculated by density functional theory are investigated as descriptors. The binding energies are close for the Cu facets, and the variation shows that two noncorrelating (orthogonal) binding energies contain up to 70% of the information from the binding energies. Further, structural analysis allows us to uniquely identify the (100)x(110) step sites as specific ethanol-producing sites from the CO2 reduction reaction

The direct CO2 electrochemical reduction reaction (CO2RR) into carbon-based chemicals has attracted tremendous attention as a sustainable process for CO2 utilization. The viability of the process, however, is contingent on finding efficient catalysts based on earth abundant elements. Carbon-based solid catalyst materials doped with nitrogen and transition metals (M-N-C) have emerged as a cost-efficient alternative for the direct electrochemical reduction of CO2 into CO. These materials contain different N functionalities and MNx moieties which could be involved in the catalytic process. With the aim of gaining insight into the role of these different active sites and how to control their concentration we have prepared 5 polyaniline derived FeNC catalysts by changing the temperature of the heat treatment (750-1050 degrees C). We observed that it is possible to tune the ratio of the different N functionalities by changing the pyrolysis temperature. Furthermore, this had a clear impact on the catalytic performance of this family of FeNC materials. In particular, a higher temperature correlated with a larger FeNx concentration resulting in a high selectivity toward the CO2RR. These results indicate that FeNx moieties play a predominant role in the catalytic process and that the incorporation of such sites to the carbon structure is enhanced by the heat-treatment temperature.

Different bismuth oxyiodide materials (BiOI, Bi4O5I2, Bi7O9I3 and Bi5O7I) were synthesized via the solvothermal method. For BiOI, microspheres (M.S.) and nanocrystals were obtained. Decrease in the iodine loading was achieved by varying the synthesis conditions, such as the solvent, temperature and heating time. Gold metallic nanoparticles were deposited on the surface of the BixOyIz materials via the deposition precipitation route. The physical, chemical, optic and electrochemical properties of the obtained materials were assessed and compared, finding notable structural and optoelectric changes as the loading of iodine decreased in the semiconductor. In fact, lessening the iodine loading resulted, not only in the increase of the band gap value, but in the shift of the valence band toward more oxidative potential. In contrast, no changes in the semiconductor properties of the BixOyIz materials were observed upon the deposition of metallic Au nanoparticles. Regarding the photocatalytic activity, the use of BiOI M.S. led to the highest degradation and mineralization rate of the antibiotic oxytetracycline (OTC) upon 5 h of visible light irradiation. Deposition of Au nanoparticles reduced the photo activity of the materials, even when low metal loadings were tested. BiOI M.S. showed certain stability throughout three consecutive reactions cycles. High photocatalytic performance was observed when environmentally relevant conditions -i.e., tap water and C-o = 50 mu g/L- were tested. Through mass spectrometry some degradation intermediaries were identified and a photocatalytic degradation route of OTC was proposed.

We report a joint experimental-computational mechanistic study of electrochemical reduction of CO2 to CH4, catalyzed by solid-state Fe-N-C catalysts, which feature atomically dispersed, catalytically active Fe-N-x sites and represent one of the very rare examples of solid, non-Cu-based electrocatalysts that yield hydrocarbon products. Work reported here focuses on the identification of plausible mechanistic pathways from CO2 to various C-1 products including methane. It is found that Fe-N-x sites convert only CO, CO2 and CH2O into methane, whereas CH3OH appears to be an end product. Distinctly different pH dependence of the catalytic CH4 evolution from CH2O in comparison with that of CO2 and CO reduction indicates differences in the proton participation of rate-determining steps. By comparing the experimental observations with density functional theory derived free energy diagrams of reactive intermediates along the CO2 reduction reaction coordinates, we unravel the dominant mechanistic pathways and roles of CO and CH2O during the catalytic CO2-to-CH4 cascades and their rate-determining steps. We close with a comprehensive reaction network of CO2RR on single-site Fe-N-C catalysts, which may prove useful in developing efficient, non-Cubased catalysts for hydrocarbon production.

The electrochemical CO2 reduction reaction (CO2RR) is a promising technology for converting waste CO2 into chemicals which could be used as feedstock for the chemical industry or as synthetic fuels. The technological viability of this process, however, is contingent on finding affordable and efficient catalysts. Recently, carbon-based solid state catalyst materials containing small amounts of nitrogen and transition metals (MNC) have emerged as a selective and cost-efficient alternative to noble metal catalysts for the direct electrochemical reduction of CO2 into CO. In addition, other products have also been reported, including formic acid and methane. In this Perspective, we offer a focused discussion of recent advances in the field of MNC catalysts for the CO2RR. The different factors which control the catalytic performance of MNC toward the CO2RR are discussed in this Perspective. We focus on density functional theory-guided experimental studies aiming to elucidate key experimental parameters and molecular descriptors that control the activity and selectivity of this class of materials. We close addressing the remaining challenges and take a look forward into future studies.