Electrocatalytic transformation of carbon dioxide (CO2) and water into chemical feedstocks offers the potential to reduce carbon emissions by shifting the chemical industry away from fossil fuel dependence. We provide a technoeconomic and carbon emission analysis of possible products, offering targets that would need to be met for economically compelling industrial implementation to be achieved. We also provide a comparison of the projected costs and CO2 emissions across electrocatalytic, biocatalytic, and fossil fuel–derived production of chemical feedstocks. We find that for electrosynthesis to become competitive with fossil fuel–derived feedstocks, electrical-to-chemical conversion efficiencies need to reach at least 60%, and renewable electricity prices need to fall below 4 cents per kilowatt-hour. We discuss the possibility of combining electro- and biocatalytic processes, using sequential upgrading of CO2 as a representative case. We describe the technical challenges and economic barriers to marketable electrosynthesized chemicals.Science, this issue p. eaav3506

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Platinum group metal-free (PGM-free) metal-nitrogen-carbon catalysts have emerged as a promising alternative to their costly platinum (Pt)-based counterparts in polymer electrolyte fuel cells (PEFCs) but still face some major challenges, including (i) the identification of the most relevant catalytic site for the oxygen reduction reaction (ORR) and (ii) demonstration of competitive PEFC performance under automotive-application conditions in the hydrogen (H)-air fuel cell. Herein, we demonstrate H-air performance gains achieved with an iron-nitrogen-carbon catalyst synthesized with two nitrogen precursors that developed hierarchical porosity. Current densities recorded in the kinetic region of cathode operation, at fuel cell voltages greater than ~0.75 V, were the same as those obtained with a Pt cathode at a loading of 0.1 milligram of Pt per centimeter squared. The proposed catalytic active site, carbon-embedded nitrogen-coordinated iron (FeN), was directly visualized with aberration-corrected scanning transmission electron microscopy, and the contributions of these active sites associated with specific lattice-level carbon structures were explored computationally.

This paper gives a comprehensive review about the most recent progress in synthesis, characterization, fundamental understanding, and the performance of graphene and graphene oxide sponges. Practical applications are considered including use in composite materials, as the electrode materials for electrochemical sensors, as absorbers for both gases and liquids, and as electrode materials for devices involved in electrochemical energy storage and conversion. Several advantages of both graphene and graphene oxide sponges such as three dimensional graphene networks, high surface area, high electro/ thermo conductivities, high chemical/electrochemical stability, high flexibility and elasticity, and extremely high surface hydrophobicity are emphasized. To facilitate further research and development, the technical challenges are discussed, and several future research directions are also suggested in this paper. Broader contextAdvanced graphene materials residing at the frontier of scientic research offer immense potential for overcoming the challenges related to the performance, functionality and durability of key functional materials' in the elds of life science, energy, and the environment. Future demand necessitates advanced processing methods be developed that can mass produce high quality, two-dimensional graphene sheets while overcoming the issues of poor dispersion and restacking with large size-scale deployment of two-dimensional graphene sheets. These issues, along with graphene sheet defects and multilayer thicknesses prevent the full realization of graphene's high potential, including electronic properties and high surface area. Three-dimensional arrangements have been recently able to address these limitations, by creating sponge-like low density materials with a long list of benecial properties including: macroscale size, high accessible surface area, less restacking, highly-interconnected microstructure, high strength and exibility, fast ion transport and electron conductivity. This review is intended to address the continued developments and challenges with a wide scope of interest, highlighting fundamental understanding of the synthesis and characterization procedures, future outlook, as well as an in-depth discussion of application areas reporting high performance in recent publications. The outstanding potential of these materials has enabled signicant enhancements for numerous important applications such as electrochemical energy storage and conversion, absorption, sensing, catalysis, transistors and polymer composites.

Significant advances have been made in recent years discovering new electrocatalysis and developing a fundamental understanding of electrochemical CO 2 reduction processes. This field has progressed to the point that efforts can now focus on translating this knowledge towards the development of practical CO 2 electrolyzers, which have the potential to replace conventional petrochemical processes as a sustainable route to produce fuels and chemicals. In this perspective, we take a critical look at the progress in incorporating electrochemical CO 2 reduction catalysts into practical device architectures that operate using vapor-phase CO 2 reactants, thereby overcoming intrinsic limitations of aqueous-based systems. Performance comparison is made between state-of-the-art CO 2 electrolyzers and commercial H 2 O electrolyzers-a well-established technology that provides realistic performance targets. Beyond just higher rates, vapor-fed reactors represent new paradigms for unprecedented control of local reaction conditions, and we provide a perspective on the challenges and opportunities for generating fundamental knowledge and achieving technological progress towards the development of practical CO 2 electrolyzers. TOC Image H 2 O+ CO 2 Fuels Chemicals Gas-Diffusion Electrode

Understanding the surface reactivity of CO, which is a key intermediate during electrochemical CO 2 reduction, is crucial for the development of catalysts that selectively target desired products for the conversion of CO 2 to fuels and chemicals. In this study, a customdesigned electrochemical cell is utilized to investigate planar polycrystalline copper as an electrocatalyst for CO reduction under alkaline conditions. Seven major CO reduction products have been observed including various hydrocarbons and oxygenates which are also common CO 2 reduction products, strongly indicating that CO is a key reaction intermediate for these further-reduced products. A comparison of CO and CO 2 reduction demonstrates that there is a large decrease in the overpotential for C−C coupled products under CO reduction conditions. The effects of CO partial pressure and electrolyte pH are investigated; we conclude that the aforementioned large potential shift is primarily a pH effect. Thus, alkaline conditions can be used to increase the energy efficiency of CO and CO 2 reduction to C−C coupled products, when these cathode reactions are coupled to the oxygen evolution reaction at the anode. Further analysis of the reaction products reveals common trends in selectivity that indicate both the production of oxygenates and C−C coupled products are favored at lower overpotentials. These selectivity trends are generalized by comparing the results on planar Cu to current state-of-the-art high-surface-area Cu catalysts, which are able to achieve high oxygenate selectivity by operating at the same geometric current density at lower overpotentials. Combined, these findings outline key principles for designing CO and CO 2 electrolyzers that are able to produce valuable C−C coupled products with high energy efficiency.

In this study we control the surface structure of Cu thin-film catalysts to probe the relationship between active sites and catalytic activity for the electroreduction of CO 2 to fuels and chemicals. Here, we report physical vapor deposition of Cu thin films on large-format (∼6 cm 2 ) single-crystal substrates, and confirm epitaxial growth in the <100>, <111>, and <751> orientations using X-ray pole figures. To understand the relationship between the bulk and surface structures, in situ electrochemical scanning tunneling microscopy was conducted on Cu(100), (111), and (751) thin films. The studies revealed that Cu(100) and (111) have surface adlattices that are identical to the bulk structure, and that Cu(751) has a heterogeneous kinked surface with (110) terraces that is closely related to the bulk structure. Electrochemical CO 2 reduction testing showed that whereas both Cu(100) and (751) thin films are more active and selective for C-C coupling than Cu(111), Cu(751) is the most selective for >2e− oxygenate formation at low overpotentials. Our results demonstrate that epitaxy can be used to grow singlecrystal analogous materials as large-format electrodes that provide insights on controlling electrocatalytic activity and selectivity for this reaction.carbon dioxide reduction | epitaxy | electrocatalysis | copper T he electrochemical reduction of CO 2 (CO 2 R) is a process that could couple to renewable energy from wind and solar to directly produce fuels and chemicals in a sustainable manner. However, developing catalysts is a major challenge for this reaction, and significant advances are needed to overcome the issues of poor energy efficiency and product selectivity. One reason for these issues is that there are a limited number of catalysts that can effectively convert CO 2 to products that require more than two electrons (>2e − products), e.g., methane, methanol, ethylene, etc. (1, 2). Therefore, developing catalysts that are effective for CO 2 R to >2e − products would greatly improve prospects for utilization, and such an endeavor requires a deeper understanding of the relevant surface chemistry.Out of the polycrystalline metals, Cu is the only one that has shown a propensity for CO 2 R to >2e − products at considerable rates and selectivity (2, 3). To date, its uniqueness is reflected by how nearly all work on catalysts with improved activity and selectivity for >2e − products is based on Cu (4-6). However, polycrystalline Cu is not particularly selective toward any one >2e − reduction product (7). Thus, it is critical to understand what active site motifs lead to this unique selectivity for further reduced products and to apply this knowledge to develop new materials with this electrocatalytic behavior.Single-crystal studies on Cu have shown that CO 2 R activity and selectivity are extremely sensitive to surface structure. In particular, facet sensitivities for C-C coupling are the most widely studied, with experimental reports concluding that Cu(100) terraces and any orientation of step sites are more...

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