CO2 Reduction of Hybrid Cu2 O-Cu/Gas Diffusion Layer Electrodes and their Integration in a Cu-based Photoelectrocatalytic Cell

Construction synergetic adsorption and activation surface via confined Cu/Cu2O and Ag nanoparticles on TiO2 for effective conversion of CO2 to CH4

High-performance photocatalysts for catalytic reduction of CO2 are largely impeded by inefficient charge separation and surface activity. Reasonable design and efficient collaboration of multiple active sites are important for attaining high reactivity and product selectivity. Herein, Cu-Cu2O and Ag nanoparticles are confined as dual sites for assisting CO2 photoreduction to CH4 on TiO2. The introduction of Cu-Cu2O leads to an all-solid-state Z-scheme heterostructure on the TiO2 surface, which achieves efficient electron transfer to Cu2O and adsorption and activation of CO2. The confined nanometallic Ag further enhances the carrier's separation efficiency, promoting the conversion of activated CO2 molecules to •COOH and further conversion to CH4. Particularly, this strategy is highlighted on the TiO2 system for a photocatalytic reduction reaction of CO2 and H2O with a CH4 generation rate of 62.5 μmol∙g-1∙h-1 and an impressive selectivity of 97.49 %. This work provides new insights into developing robust catalysts through the artful design of synergistic catalytic sites for efficient photocatalytic CO2 conversion.

Progress and perspectives on 1D nanostructured catalysts applied in photo(electro)catalytic reduction of CO2

Reducing CO₂ into value-added chemicals and fuels by artificial photosynthesis (photocatalysis and photoelectrocatalysis) is one of the considerable solutions to global environmental and energy issues. One-dimensional (1D) nanostructured catalysts (nanowires, nanorods, nanotubes and so on.) have attracted extensive attention due to their superior light-harvesting ability, co-catalyst loading capacity, and high carrier separation rate. This review analyzed the basic principle of the photo(electro)catalytic CO₂ reduction reaction (CO₂ RR) briefly. The preparation methods and properties of 1D nanostructured catalysts are introduced. Next, the applications of 1D nanostructured catalysts in the field of photo(electro)catalytic CO₂ RR are introduced in detail. In particular, we introduced the design of composite catalysts with 1D nanostructures, for example loading 0D, 1D, 2D, and 3D materials on a 1D nanostructured semiconductor to construct a heterojunction to optimize the photo-response range, carrier separation and transport efficiency, CO₂ adsorption and activation capacity, and stability of the catalyst. Finally, the development prospects of 1D nanostructured catalysts are discussed and summarized. This review can provide guidance for the rational design of advanced catalysts for photo(electro)catalytic CO₂ RR.

Shape-Dependent Performance of Cu/Cu2 O for Photocatalytic Reduction of CO2

The photocatalytic conversion of CO₂ into solar fuels or chemicals is a sustainable approach to relieve the immediate problems related to global warming and the energy crisis. This study concerns the effects of morphological control on a Cu/Cu₂ O-based photocatalyst for CO₂ reduction. The as-synthesized spherical Cu/Cu₂ O photocatalyst exhibits higher activity than the octahedral one under visible light irradiation. The difference in photocatalytic performance between these two catalysts could be attributed to the following two factors: (1) The multifaceted structure of spherical Cu/Cu₂ O favors charge separation; (2) octahedral Cu/Cu₂ O only contains more positively charged (111) facets, which are unfavorable for CO₂ photoreduction. The results further highlight the importance of utilizing crystal facet engineering to further improve the performance of CO₂ reduction photocatalysts.

Nanostructured Copper-Based Electrodes Electrochemically Synthesized on a Carbonaceous Gas Diffusion Membrane with Catalytic Activity for the Electroreduction of CO2

In this work, four different 4 cm2-sized nanostructured Cu-based electrocatalysts have been designed by a one-step electrodeposition process of Cu metal on a three-dimensional carbonaceous membrane. One consisted of Cu0, and the other three were obtained by further simple oxidative treatments. Morphological, structural, and electrochemical investigations on the four materials were carried out by scanning electron microscopy, Raman spectroscopy, X-ray diffraction, linear sweep voltammetry, and potential-controlled electrolysis. All the electrocatalysts showed promising catalytic activities toward CO2 electroreduction in liquid phase, with a remarkable selectivity toward acetic acid achieved when using the oxidized materials. In particular, the best electrocatalytic activity was observed for the Cu2O-Cu0 catalyst, working at a relatively low potential (-0.4 V vs RHE), which exhibited a stable and low current density of 0.46 mA cm-2 and a productivity of 308 μmol gcat-1 h-1. These results were attributed to the nanostructured morphology that is characterized by many void spaces and by a high surface area, which should guarantee a large number of CuI and Cu0 catalytic active sites. Moreover, kinetic analyses and preliminary studies about catalyst regeneration highlighted the stability of the best-performing catalyst.

Multisample Correlation Reveals the Origin of the Photocurrent of an Unstable Cu2O Photocathode during CO2 Reduction

The reliable characterization of the photoelectrochemical (PEC) performance of unstable photoelectrodes, often the simplest devices used as a baseline, is a huge challenge. By performing a correlation analysis of more than 100 parameters of Cu₂O photocathodes electrodeposited under the same conditions, we discovered a strong positive correlation (R = 0.866) between the photocurrent in argon and the deposition current peak magnitude during electrodeposition, while a strong negative correlation (R = -0.787) was found in CO₂. In argon, a positive correlation between the photocurrent during PEC tests and the post-PEC dark current suggests the dominance of photodegradation. In CO₂, the higher photocurrent in PEC tests correlates well with the lower post-PEC dark current, revealing the dominance of photocatalytic CO₂ reduction during the rapid PEC tests. Correlation analysis provides statistically robust insights into the operation of unstable electrodes based on routinely measured parameters and thus constitutes a simple yet previously unexplored methodology for characterizing photoelectrodes within the first minutes of operation.

Efficient photoelectrochemical CO2 conversion for selective acetic acid production

Amidst the development of photoelectrochemical (PEC) CO₂ conversion toward practical application, the production of high-value chemicals beyond C₁ compounds under mild conditions is greatly desired yet challenging. Here, through rational PEC device design by combining Au-loaded and N-doped TiO₂ plate nanoarray photoanode with Zn-doped Cu₂O dark cathode, efficient conversion of CO₂ to CH₃COOH has been achieved with an outstanding Faradaic efficiency up to 58.1% (91.5% carbon selectivity) at 0.5 V vs. Ag/AgCl. Temperature programmed desorption and in situ Raman spectra reveal that the Zn-dopant in Cu₂O plays multiple roles in selective catalytic CO₂ conversion, including local electronic structure manipulation and active site modification, which together promote the formation of intermediate *CH₂/*CH₃ for C-C coupling. Apart from that, it is also unveiled that the sufficient electron density provided by the Au-loaded and N-doped TiO₂ plate nanoarray photoanode plays an equally important role by initiating multi-electron CO₂ reduction. This work provides fresh insights into the PEC system design to reach the multi-electron reduction reaction and facilitate the C-C coupling reaction toward high-value multicarbon (C₂₊) chemical production via CO₂ conversion.

Recent Advances in Solar-Driven Carbon Dioxide Conversion: Expectations versus Reality

Solar-driven carbon dioxide (CO₂) conversion to fuels and high-value chemicals can contribute to the better utilization of renewable energy sources. Photosynthetic (PS), photocatalytic (PC), photoelectrochemical (PEC), and photovoltaic plus electrochemical (PV+EC) approaches are intensively studied strategies. We aimed to compare the performance of these approaches using unified metrics and to highlight representative studies with outstanding performance in a given aspect. Most importantly, a statistical analysis was carried out to compare the differences in activity, selectivity, and durability of the various approaches, and the underlying causes are discussed in detail. Several interesting trends were found: (i) Only the minority of the studies present comprehensive metrics. (ii) The CO₂ reduction products and their relative amount vary across the different approaches. (iii) Only the PV+EC approach is likely to lead to industrial technologies in the midterm future. Last, a brief perspective on new directions is given to stimulate discussion and future research activity.

Curtailing the Overpotential of Li-CO2 Batteries with Shape-Controlled Cu2 O as Cathode: Effect of Illuminating the Cathode

Li-air batteries are limited to lab-scale research owing to the uninterrupted formation of discharge products. In the case of Li-CO₂ batteries, the increase in overpotential caused by Li₂ CO₃ formation results in cell death. In this study, Cu₂ O crystals having three different types of shapes (i.e., cubic, octahedral, and rhombic) were synthesized to compare their catalytic activity toward CO₂ reactions. The full-cycle and long-term stability test revealed that rhombohedral Cu₂ O facilitates Li₂ CO₃ decomposition more efficiently than that of cubic and octahedral Cu₂ O. The cycle was extended to investigate the photocatalytic activity of the rhombic Cu₂ O by illuminating the cell. The repeated cycles to 1 h showed a maximum overpotential of 1.5 V, which is 0.5 V lower than that of the cell without illumination. A postmortem analysis of the cell after dividing the cycles into segments demonstrated interesting results concerning the role of light and Cu₂ O during the cell cycle.