The electrocatalytic reduction of CO2 on Au-Pt bimetallic catalysts with different compositions was evaluated, offering a platform for uncovering the correlation between the catalytic activity and the surface composition of bimetallic electrocatalysts. The Au-Pt alloy films were synthesized by a magnetron sputtering co-deposition technique with tunable composition. It was found that the syngas ratio (CO:H2) on the Au-Pt films is able to be tuned by systematically controlling the binary composition. This tunable catalytic selectivity is attributed to the variation of binding strength of COOH and CO intermediates, influenced by the surface electronic structure (d-band center energy) which is linked to the surface composition of the bimetallic films. Notably, a gradual shift of the d-band center away from the Fermi level was observed with increasing Au content, which correspondingly reduces the binding strength of the COOH and CO intermediates, leading to the distinct catalytic activity for the reduction of CO2 on the compositionally variant Au-Pt bimetallic films. In addition, the formation of formic acid in the bimetallic systems at reduced overpotentials and higher yield indicates that synergistic effects can facilitate reaction pathways for products that are not accessible with the individual components.@en

CO 2 electroreduction is a promising technology to produce chemicals and fuels from renewable resources. Polycrystalline and nanostructured metals have been tested extensively while less effort has been spent on understanding the performance of bimetallic alloys. In this work, we study compositionally variant, smooth Au-Pd thin film alloys to discard any morphological or mesoscopic effect on the electrocatalytic performance. We find that the onset potential of CO formation exhibits a strong dependence on the Pd content of the alloys. Strikingly, palladium, a hydrogen evolution catalyst with reasonable exchange current density, suppresses hydrogen evolution when alloyed with gold in the presence of CO 2 . Cyclic voltammetry, in situ surface enhanced infrared absorption spectroscopy, and potential-dependent online product analysis strongly suggest that by alloying Au with Pd a significant increase in the surface coverage of adsorbed CO occurs with increasing Pd content at low overpotentials (e.g., approximately -0.35 V vs RHE). Such an increase in CO coverage suppresses H 2 evolution due to the lack of vacant active sites. Moreover, the overall increase in the binding energy with the CO 2 intermediates gained with the addition of Pd increases the CO production at low overpotentials, where polycrystalline Au suffers from poor CO 2 adsorption and poor selectivity for CO production. These results show that promising CO 2 reduction electrode materials (e.g., Au) can be alloyed not only to tune the catalyst's activity but also to deliberately decrease the availability of surface sites for competitive H 2 evolution. @en

In this work, the effect of Cu nanowire morphology on the selective electrocatalytic reduction of CO2 is presented. Cu nanowire arrays were prepared through a two-step synthesis of Cu(OH)2 and CuO nanowire arrays on Cu foil substrates and a subsequent electrochemical reduction of the CuO nanowire arrays to Cu nanowire arrays. By this simple synthesis method, Cu nanowire array electrodes with different length and density were able to be controllably synthesized. We show that the selectivity for hydrocarbons (ethylene, n-propanol, ethane, and ethanol) on Cu nanowire array electrodes at a fixed potential can be tuned by systematically altering the Cu nanowire length and density. The nanowire morphology effect is linked to the increased local pH in the Cu nanowire arrays and a reaction scheme detailing the local pH-induced formation of C2 products is also presented by a preferred CO dimerization pathway. Catalytic activity: A Cu nanowire array for CO2 reduction was developed. The length and density of the Cu nanowire array could be altered by a simple electroetching method. With varying length and density of the nanowire the chemical selectivity for CO2 reduction could be systematically tuned. The results provide experimental evidence for a nanostructure-dependent catalytic activity.@en

The electrochemical conversion of CO2 into carbon-based fuels has attracted considerable attention as a promising strategy for closing the anthropogenic carbon cycle. A key challenge for achieving this goal is to develop selective, stable, and efficient electrocatalysts for the electrocatalytic reduction of CO2. Nanostructured catalysts can provide many advantages compared to bulk materials, including the increase of active sites, the change of the local pH of the electrolyte, and improved stability. This chapter reviews the recent development of nanostructured metal catalysts for the electrocatalytic reduction of CO2, mainly focusing on the fabrication, characterization, catalytic performance, and the reaction mechanism of these materials. In addition, the recent utilization of nanostructured bimetallic catalysts are introduced and a fundamental understanding of the reaction mechanism for their ability to reduce CO2 is discussed. Finally, nanostructured carbon is shortly reviewed due to its low cost and improved catalytic activity and stability for the electroreduction of CO2.@en

In this work, the selective electrocatalytic reduction of carbon dioxide to carbon monoxide on oxide-derived silver electrocatalysts is presented. By a simple synthesis technique, the overall high faradaic efficiency for CO production on the oxide-derived Ag was shifted by more than 400 mV towards a lower overpotential compared to that of untreated Ag. Notably, the Ag resulting from Ag oxide is capable of electrochemically reducing CO2to CO with approximately 80 % catalytic selectivity at a moderate overpotential of 0.49 V, which is much higher than that (ca. 4 %) of untreated Ag under identical conditions. Electrokinetic studies show that the improved catalytic activity is ascribed to the enhanced stabilization of COOH.intermediate. Furthermore, highly nanostructured Ag is likely able to create a high local pH near the catalyst surface, which may also facilitate the catalytic activity for the reduction of CO2with suppressed H2evolution.@en

A recently discovered photodecarboxylase from Chlorella variabilis NC64A ( CvFAP) bears the promise for the efficient and selective synthesis of hydrocarbons from carboxylic acids. CvFAP, however, exhibits a clear preference for long-chain fatty acids thereby limiting its broad applicability. In this contribution, we demonstrate that the decoy molecule approach enables conversion of a broad range of carboxylic acids by filling up the vacant substrate access channel of the photodecarboxylase. These results not only demonstrate a practical application of a unique, photoactivated enzyme but also pave the way to selective production of short-chain alkanes from waste carboxylic acids under mild reaction conditions.@en

We report the preparation and electrocatalytic performance of silver-containing gas diffusion electrodes (GDEs) derived from a silver coordination polymer (Ag-CP). Layer-by-layer growth of the Ag-CP onto porous supports was applied to control Ag loading. Subsequent electro-decomposition of the Ag-CP resulted in highly selective and efficient CO2-to-CO GDEs in aqueous CO2 electroreduction. Afterward, the metal-organic framework (MOF)-mediated approach was transferred to a gas-fed flow electrolyzer for high current density tests. The in situ formed GDE, with a low silver loading of 0.2 mg cm-2, showed a peak performance of jCO ≈ 385 mA cm-2 at around -1.0 V vs RHE and stable operation with high FECO (>96%) at jTotal = 300 mA cm-2 over a 4 h run. These results demonstrate that the MOF-mediated approach offers a facile route for manufacturing uniformly dispersed Ag catalysts for CO2 electrochemical reduction by eliminating ill-defined deposition steps (drop-casting, etc.) while allowing control of the catalyst structure through self-assembly.@en

The electrocatalytic conversion of CO2 into fuel and valuable chemicals by coupling with a renewable electricity source is a promising strategy for closing the anthropogenic carbon cycle. The critical step for achieving this practical CO2 utilization is to find a suitable electrocatalyst that is capable of reducing CO2 in a cost-effective process with high efficiency, stability and selectivity for a desired product...@en

In this work, the highly selective and stable electrocatalytic reduction of CO2 to CO on nanostructured Ag electrocatalysts is presented. The Ag electrocatalysts are synthesized by the electroreduction of Ag2CO3 formed by in situ anodic-etching of Ag foil in a KHCO3 electrolyte. After 3 min of this etching treatment, the Ag2CO3-derived nanostructured Ag electrocatalysts are capable of producing CO with up to 92% Faradaic efficiency at an overpotential as low as 290 mV, which surpasses all of the reported Ag catalysts at identical conditions to date. In addition, the anodic-etched Ag retained ∼90% catalytic selectivity in the electroreduction of CO2 to CO for more than 100 h. The Ag2CO3-derived Ag is able to facilitate the activation of CO2 via reduction of the activation energy barrier of the initial electron transfer and provide an increased number of active sites, resulting in the dramatically improved catalytic activity for the reduction of CO2 to CO.@en

Electrochemical CO2 reduction can convert CO2 into fuels and valuable chemicals using renewable electricity, which provides a prospective path toward large-scale energy storage. Au nanostructured electrodes have demonstrated the best catalytic performance for CO2 conversion: high catalytic selectivity for CO formation at low overpotentials, high current density, and long-term durability. Here, we report selective electrocatalytic CO2 reduction to CO on nanostructured Au with various morphologies, prepared via electrocrystallization with a megahertz potential oscillation. X-ray diffraction showed that the proportion of {100} and {110} to {111} surfaces increased at more negative deposition potentials. Cyclic voltammetry showed the potential of zero charge on an Au film was approximately 0.35 V vs standard hydrogen electrode (SHE) and that the surface energy decreased by ∼1 eV/nm2 at -0.5 V vs SHE, tending to 0 within several volts in either direction. Scanning electron micrograms showed that the Au crystals grow primarily in the 〈110〉 directions. From these data, a model for crystallization from melts was adapted to calculate the roughening temperature of the {111}, {100}, and {110} Miller indices as 7000, 4000, and 1000 K, decreasing for more negative deposition potentials. This offers a framework for exposed facet control in electrocrystallization. In CO2 electrocatalysis, -0.35 V vs reversible hydrogen electrode was observed to be a turn-on potential for improved CO2 reduction activity; dendrites showed 50% Faradaic efficiency for CO production at more cathodic potentials. The Tafel slope was measured to be 40 mV/decade for {100} and {110}-rich Au dendrites and 110 mV/decade for {111}-dominated Au plates, suggesting the higher surface energy crystal facets may stabilize all of the CO2 reduction reaction intermediates.@en

Electrochemical CO2 reduction can convert CO2 into fuels and valuable chemicals using renewable electricity, which provides a prospective path toward large-scale energy storage. Au nanostructured electrodes have demonstrated the best catalytic performance for CO2 conversion: high catalytic selectivity for CO formation at low overpotentials, high current density, and long-term durability. Here, we report selective electrocatalytic CO2 reduction to CO on nanostructured Au with various morphologies, prepared via electrocrystallization with a megahertz potential oscillation. X-ray diffraction showed that the proportion of {100} and {110} to {111} surfaces increased at more negative deposition potentials. Cyclic voltammetry showed the potential of zero charge on an Au film was approximately 0.35 V vs standard hydrogen electrode (SHE) and that the surface energy decreased by ∼1 eV/nm2 at -0.5 V vs SHE, tending to 0 within several volts in either direction. Scanning electron micrograms showed that the Au crystals grow primarily in the 〈110〉 directions. From these data, a model for crystallization from melts was adapted to calculate the roughening temperature of the {111}, {100}, and {110} Miller indices as 7000, 4000, and 1000 K, decreasing for more negative deposition potentials. This offers a framework for exposed facet control in electrocrystallization. In CO2 electrocatalysis, -0.35 V vs reversible hydrogen electrode was observed to be a turn-on potential for improved CO2 reduction activity; dendrites showed 50% Faradaic efficiency for CO production at more cathodic potentials. The Tafel slope was measured to be 40 mV/decade for {100} and {110}-rich Au dendrites and 110 mV/decade for {111}-dominated Au plates, suggesting the higher surface energy crystal facets may stabilize all of the CO2 reduction reaction intermediates.@en

Photoelectrochemical (PEC) water splitting is a sustainable approach to produce a renewable fuel by harvesting the energy of the Sun to split water to form hydrogen and oxygen. In order to drive the water splitting reaction efficiently, substantial ohmic losses due to poor ionic conductivity of the electrolyte should be avoided, and therefore the reaction should be carried out at an extreme electrolyte pH. Herein we demonstrate the photoelectrochemical activity of an amorphous silicon carbide (a-SiC) photocathode for solar hydrogen evolution using an ultrathin nickel (Ni) film coupled with a nickel molybdenum catalyst (Ni-Mo) in a highly alkaline solution (pH 14). The incorporation of the Ni film coupled with Ni-Mo nanoparticles increases the number of active sites and therefore improves the kinetics of the hydrogen evolution reaction. Additionally, we report the influence of the catalyst configurations on the ohmic and solid liquid junction behavior on semiconducting interfacial layers. The a-SiC photocathode coated with the Ni/Ni-Mo dual-catalyst produces a photocurrent density of -14 mA cm-2 at 0 V vs. RHE using only cheap and abundant materials. This photocurrent is the highest recorded value from an amorphous-Si-based photocathode, and is achieved with a total film thickness of less than 150 nm.@en

Photoelectrochemical (PEC) water splitting is a sustainable approach to produce a renewable fuel by harvesting the energy of the Sun to split water to form hydrogen and oxygen. In order to drive the water splitting reaction efficiently, substantial ohmic losses due to poor ionic conductivity of the electrolyte should be avoided, and therefore the reaction should be carried out at an extreme electrolyte pH. Herein we demonstrate the photoelectrochemical activity of an amorphous silicon carbide (a-SiC) photocathode for solar hydrogen evolution using an ultrathin nickel (Ni) film coupled with a nickel molybdenum catalyst (Ni-Mo) in a highly alkaline solution (pH 14). The incorporation of the Ni film coupled with Ni-Mo nanoparticles increases the number of active sites and therefore improves the kinetics of the hydrogen evolution reaction. Additionally, we report the influence of the catalyst configurations on the ohmic and solid liquid junction behavior on semiconducting interfacial layers. The a-SiC photocathode coated with the Ni/Ni-Mo dual-catalyst produces a photocurrent density of -14 mA cm-2 at 0 V vs. RHE using only cheap and abundant materials. This photocurrent is the highest recorded value from an amorphous-Si-based photocathode, and is achieved with a total film thickness of less than 150 nm.@en

It is demonstrated that hydrogen treatment as a simple, effective strategy can greatly improve the broadband photo-responsive performance of pristine TiO2 nanorod arrays (NRAs)/SiO2/n-Si heterojunctions. The hydrogen-treated TiO2 NRAs/SiO2/n-Si heterojunction shows a stable, repeatable and broadband photo response from 365 nm to 980 nm at 100 μW cm-2. The responsivity (R) of H:TiO2 NRAs/SiO2/n-Si approaches the ultrahigh value of 468 A W-1 and it has an outstanding detectivity (D∗) of 1.96 × 1014 cm Hz1/2 W-1 and an excellent sensitivity (S) of 2.63 × 107 cm2 W-1, in contrast to the values of R (10-6-10-1 A W-1) or S (2 × 103 cm2 W-1) from reported TiO2 nanofilm/TiO2 NRAs/n-Si(111) photodetectors, indicating a huge responsivity enhancement of up to 4-8 orders of magnitude. Additionally, the response and recovery time are extremely short (3.5-3.9 ms). The comprehensive characteristics make the device stand out among the previously reported 1D metal oxide nanostructure/Si based photodetectors. In fact, the R, S and D∗ values of the heterojunction are 2-4 orders of magnitude higher than those of some new 2D nanomaterials/Si based photodetectors. The excellent photo-responsive performance may be attributed to the energy band structure of the TiO2@TiO2-xHx core/shell structure, the interface effect of the TiO2@TiO2-xHx/Si heterojunction, etc. This research provides a new concept for the design of other metal oxide based heterojunction photodetectors.@en

It is demonstrated that hydrogen treatment as a simple, effective strategy can greatly improve the broadband photo-responsive performance of pristine TiO2 nanorod arrays (NRAs)/SiO2/n-Si heterojunctions. The hydrogen-treated TiO2 NRAs/SiO2/n-Si heterojunction shows a stable, repeatable and broadband photo response from 365 nm to 980 nm at 100 μW cm-2. The responsivity (R) of H:TiO2 NRAs/SiO2/n-Si approaches the ultrahigh value of 468 A W-1 and it has an outstanding detectivity (D∗) of 1.96 × 1014 cm Hz1/2 W-1 and an excellent sensitivity (S) of 2.63 × 107 cm2 W-1, in contrast to the values of R (10-6-10-1 A W-1) or S (2 × 103 cm2 W-1) from reported TiO2 nanofilm/TiO2 NRAs/n-Si(111) photodetectors, indicating a huge responsivity enhancement of up to 4-8 orders of magnitude. Additionally, the response and recovery time are extremely short (3.5-3.9 ms). The comprehensive characteristics make the device stand out among the previously reported 1D metal oxide nanostructure/Si based photodetectors. In fact, the R, S and D∗ values of the heterojunction are 2-4 orders of magnitude higher than those of some new 2D nanomaterials/Si based photodetectors. The excellent photo-responsive performance may be attributed to the energy band structure of the TiO2@TiO2-xHx core/shell structure, the interface effect of the TiO2@TiO2-xHx/Si heterojunction, etc. This research provides a new concept for the design of other metal oxide based heterojunction photodetectors.@en