Solvothermally-Prepared Cu2 O Electrocatalysts for CO2 Reduction with Tunable Selectivity by the Introduction of p-Block Elements

Molecular Engineering of Copper Phthalocyanine for CO2 Electroreduction to Methane

Efficient electrochemical CO2 reduction reaction (ECO2RR) to multi-electron reductive products remains a great challenge. Herein, molecular engineering of copper phthalocyanines (CuPc) was explored by modifying electron-withdrawing groups (EWGs) (cyano, sulfonate anion) and electron-donating groups (EDGs) (methoxy, amino) to CuPc, then supporting onto carbon paper or carbon cloth by means of droplet coating, loading with carbon nanotubes and coating in polypyrrole (PPy). The results showed that the PPy-coated CuPc effectively catalysed ECO2RR to CH4. Interestingly, experimental results and DFT calculations indicated EWGs markedly improved the selectivity of methane for the reason that the introduction of EWGs reduces electron density of catalytic active center, resulting in a positive move to initial reduction potential. Otherwise, the modification of EDGs significantly reduces the selectivity towards methane. This electronic effect and heterogenization of CuPc are facile and effective molecular engineering, benefitting the preparation of electrocatalysts for further reduction of CO2.

CO2 Electroreduction To Syngas With Tunable Composition In An Artificial Leaf

Artificial leaves (a-leaves) can reduce carbon dioxide into syngas using solar power and could be combined with thermo- and biocatalytic technologies to decentralize the production of valuable products. By providing variable CO : H2 ratios on demand, a-leaves could facilitate optimal combinations and control the distribution of products in most of these hybrid systems. However, the current design procedures of a-leaves concentrate on achieving high performance for a predetermined syngas composition. This study demonstrates that incorporating the electrolyte flow as a design variable enables flexible production without compromising performance. The concept was tested on an a-leaf using a commercial cell, a Cu2 O:Inx cathodic catalyst, and an inexpensive amorphous silicon thin-film photovoltaic module. Syngas with CO : H2 ratio in the range of 1.8-2.3 could be attained with only 2 % deviation from the optimal cell voltage and controllable solely by catholyte flow. These features could be beneficial for downstream technologies such as Fischer-Tropsch synthesis and anaerobic fermentation.

Facile and Stable CuInO2 Nanoparticles for Efficient Electrochemical CO2 Reduction

Searching for electrocatalysts for the electrochemical CO2 reduction reaction (e-CO2RR) with high selectivity and stability remains a significant challenge. In this study, we design a Cu-CuInO2 composite with stable states of Cu0/Cu+ by electrochemically depositing indium onto CuCl-decorated Cu foil. The catalyst displays superior selectivity toward the CO product, with a maximal Faraday efficiency of 89% at -0.9 V vs the reversible hydrogen electrode, and maintains impressive stability up to 27 h with a retention rate of >76% in Faraday efficiency. Our systematical characterizations reveal that the catalyst's high performance is attributed to CuInO2 nanoparticles. First-principles calculations further confirm that CuInO2(012) is more conducive to CO generation than Cu(111) under applied potential and presents a higher energy barrier than Cu(111) for the hydrogen evolution reaction. These theoretical predictions are consistent with our experimental observations, suggesting that CuInO2 nanoparticles offer a facile catalyst with a high selectivity and stability for e-CO2RR.

CO Electroreduction Mechanism on Single-Atom Zn (101) Surfaces: Pathway to C2 Products

Electrocatalytic reduction of carbon dioxide (CO₂RR) employs electricity to store renewable energy in the form of reduction products. The activity and selectivity of the reaction depend on the inherent properties of electrode materials. Single-atom alloys (SAAs) exhibit high atomic utilization efficiency and unique catalytic activity, making them promising alternatives to precious metal catalysts. In this study, density functional theory (DFT) was employed to predict stability and high catalytic activity of Cu/Zn (101) and Pd/Zn (101) catalysts in the electrochemical environment at the single-atom reaction site. The mechanism of C2 products (glyoxal, acetaldehyde, ethylene, and ethane) produced by electrochemical reduction on the surface was elucidated. The C-C coupling process occurs through the CO dimerization mechanism, and the formation of the *CHOCO intermediate proves beneficial, as it inhibits both HER and CO protonation. Furthermore, the synergistic effect between single atoms and Zn results in a distinct adsorption behavior of intermediates compared to traditional metals, giving SAAs unique selectivity towards the C2 mechanism. At lower voltages, the Zn (101) single-atom alloy demonstrates the most advantageous performance in generating ethane on the surface, while acetaldehyde and ethylene exhibit significant certain potential. These findings establish a theoretical foundation for the design of more efficient and selective carbon dioxide catalysts.

A Critical Study of Cu2O: Synthesis and Its Application in CO2 Reduction by Photochemical and Electrochemical Approaches

Copper oxide (Cu2O) is a potential material as a catalyst for CO2 reduction. Cu2O nanostructures have many advantages, including interfacial charge separation and transportation, enhanced surface area, quantum efficiency, and feasibility of modification via composite development or integration of the favorable surface functional groups. We cover the current advancements in the synthesis of Cu2O nanomaterials in various morphological dimensions and their photochemical and electrochemical applications, which complies with the physical enrichment of their enhanced activity in every application they are employed in. The scope of fresh designs, namely composites or the hierarchy of copper oxide nanostructures, and various ways to improve CO2 reduction performance are also discussed in this review. Photochemical and electrochemical CO2 transformations have received tremendous attention in the last few years, thanks to the growing interest in renewable sources of energy and green facile chemistry. The current review provides an idea of current photochemical and electrochemical carbon dioxide fixing techniques by using Cu2O-based materials. Carboxylation and carboxylative cyclization, yield valuable chemicals such as carboxylic acids and heterocyclic compounds. Radical ions, which are induced by photo- and electrochemical reactions, as well as other high-energy organic molecules, are regarded as essential mid-products in photochemical and electrochemical reactions with CO2. It has also been claimed that CO2 can be activated to form radical anions.

Electrocatalysis for CO2 conversion: from fundamentals to value-added products

This timely and comprehensive review mainly summarizes advances in heterogeneous electroreduction of CO₂: from fundamentals to value-added products.

Stability and Degradation Mechanisms of Copper-Based Catalysts for Electrochemical CO2 Reduction

To date, copper is the only monometallic catalyst that can electrochemically reduce CO₂ into high value and energy-dense products, such as hydrocarbons and alcohols. In recent years, great efforts have been directed towards understanding how its nanoscale structure affects activity and selectivity for the electrochemical CO₂ reduction reaction (CO₂ RR). Furthermore, many attempts have been made to improve these two properties. Nevertheless, to advance towards applied systems, the stability of the catalysts during electrolysis is of great significance. This aspect, however, remains less investigated and discussed across the CO₂ RR literature. In this Minireview, the recent progress on understanding the stability of copper-based catalysts is summarized, along with the very few proposed degradation mechanisms. Finally, our perspective on the topic is given.

Structure-Tunable Copper-Indium Catalysts for Highly Selective CO2 Electroreduction to CO or HCOOH

Selectively approaching chemicals with one composition-tunable catalyst is attractive for practical manufacturing. Bimetallic copper-indium (Cu-In) catalysts have been synthesized by using a coprecipitation method and found to be among the best reported In-based catalysts for electrochemical CO₂ reduction to CO or HCOOH. By varying the metal ratio, the catalyst can be tuned from a core-shell structure that selectively produces CO to a well-mixed structure that prefers HCOOH production. The distinct selectivities depend on the structure-sensitive binding strength of key reactive intermediates. These findings can benefit the development of a broader range of selectivity-tunable catalysts.

Nitride-Derived Copper Modified with Indium as a Selective and Highly Stable Catalyst for the Electroreduction of Carbon Dioxide

The lack of efficient catalysts prevents the electrocatalytic reduction of carbon dioxide from contributing to the pressing target of a carbon-neutral economy. Indium-modified copper nitride was identified as a stable electrocatalyst selective toward CO. In2 O3 /Cu3 N showed a Faradaic efficiency of 80 % at 0.5 V overpotential for at least 50 h, in stark contrast to the very limited stability of the benchmark In2 O3 /Cu2 O. Microfabricated systems allowed to correlate activity with highly stable interfaces in indium-modified copper nitride. In contrast, fast diffusion of indium resulted in rapidly evolving interfaces in the case of the system based on oxide-derived Cu. A metastable nitrogen species observed by spectroscopic means was proposed as the underlying cause leading to the unchanging interfaces. This work reveals the stabilizing properties of nitride-derived copper toward high-performance multicomponent catalysts.

Achieving Efficient CO2 Electrochemical Reduction on Tunable In(OH)3-Coupled Cu2O-Derived Hybrid Catalysts

Tunable In(OH)₃-coupled Cu₂O-derived hybrid catalysts are facilely synthesized to boost the selectivity and efficiency of the electrochemical CO₂ reduction reaction (CO₂RR). The maximum faradaic efficiency (FE) of 90.37% for CO production is achieved at -0.8 V versus reversible hydrogen electrode. The mechanistic discussion suggests that the composition-dependent synergistic effect results in the enhanced selectivity for CO on the hybrid catalyst. By increasing the concentration of the electrolyte, a dramatically enhanced current density of 40.17 mA cm^-2 was achieved at -1.0 V in 0.7 M KHCO₃. Furthermore, a KHCO₃ electrolyte with high concentration promotes the selectivity of CO₂RR over the low overpotential range. At a low overpotential of 290 mV, the increased FE for CO of 74.05% is obtained in 0.7 M KHCO₃ as compared to that of 57.04% in 0.1 M KHCO₃. Combining with the synergistic effect of the catalyst and the concentration effect of the electrolyte, the hybrid catalyst achieves high efficiency, high selectivity, and high stability for CO₂RR.

Origin of the Selective Electroreduction of Carbon Dioxide to Formate by Chalcogen Modified Copper

The electrochemical reduction of atmospheric CO₂ by renewable electricity opens new routes to synthesize fuels and chemicals, but more selective and efficient catalysts are needed. Herein, by combining experimental and first-principles studies, we explain why chalcogen modified copper catalysts are selective toward formate as the only carbon product. On the unmodified copper, adsorbed CO₂ is the key intermediate, yielding carbon monoxide and formate as carbon products. On sulfur, selenium, or tellurium modified copper, chalcogen adatoms are present on the surface and actively participate in the reaction, either by transferring a hydride or by tethering CO₂ thus suppressing the formation of CO. These results highlight the active role of chalcogen centers via chemical steps and point toward basicity as the key descriptor for the stability and selectivity of these catalysts.

Dopant-induced electron localization drives CO2 reduction to C2 hydrocarbons

The electrochemical reduction of CO₂ to multi-carbon products has attracted much attention because it provides an avenue to the synthesis of value-added carbon-based fuels and feedstocks using renewable electricity. Unfortunately, the efficiency of CO₂ conversion to C₂ products remains below that necessary for its implementation at scale. Modifying the local electronic structure of copper with positive valence sites has been predicted to boost conversion to C₂ products. Here, we use boron to tune the ratio of Cu^δ+ to Cu⁰ active sites and improve both stability and C₂-product generation. Simulations show that the ability to tune the average oxidation state of copper enables control over CO adsorption and dimerization, and makes it possible to implement a preference for the electrosynthesis of C₂ products. We report experimentally a C₂ Faradaic efficiency of 79 ± 2% on boron-doped copper catalysts and further show that boron doping leads to catalysts that are stable for in excess of ~40 hours while electrochemically reducing CO₂ to multi-carbon hydrocarbons.

Microfabricated electrodes unravel the role of interfaces in multicomponent copper-based CO2 reduction catalysts

The emergence of synergistic effects in multicomponent catalysts can result in breakthrough advances in the electrochemical reduction of carbon dioxide. Copper-indium catalysts show high performance toward carbon monoxide production but also extensive structural and compositional changes under operation. The origin of the synergistic effect and the nature of the active phase are not well understood, thus hindering optimization efforts. Here we develop a platform that sheds light into these aspects, based on microfabricated model electrodes that are evaluated under conventional experimental conditions. The relationship among the electrode performance, geometry and composition associates the high carbon monoxide evolution activity of copper-indium catalysts to indium-poor bimetallic phases, which are formed upon exposure to reaction conditions in the vicinity of the interfaces between copper oxide and an indium source. The exploratory extension of this approach to the copper-tin system demonstrates its versatility and potential for the study of complex multicomponent electrocatalysts.

The development of efficient catalysts for electrochemical carbon dioxide conversion is hindered by a lack of rationalization. Here, authors use microfabricated electrodes to study the birth of active sites around interfaces in multicomponent copper-based catalysts during carbon dioxide reduction.