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N‐coordinated Ni sites (NiNx) are effective catalysts for the electrochemical reduction of CO2 to CO. In most researches, modulating the coordination environment of Ni atoms is focused on to improve electrochemical CO2 reduction (ECR) performance. However, the influence of the carbon substrate's structure on the intrinsic activity of NiNx is seldom investigated. The highly curved surface of carbon nanotubes (CNT) may provide a unique curvature effect on NiNx. It is found that the Ni residues in CNT can be atomized to form NiNx sites on the surface of CNT (Ni‐N/CNT@covalent triazine framework [CTF]) through high‐temperature pyrolysis, using a soluble CTF nanosheet as N precursor. The π‐conjugated and ultrathin 2D structure of CTF enables closer interfacial contact between CTF and CNT, which avoids the formation of a thick carbon layer to maximize the curvature effect. Theoretical data reveal that the NiN3 configuration may act as a highly active ECR site, and the curvature effect from CNT can further tune the electronic structure of NiN3, thus improving the ECR kinetics. The Ni‐N/CNT@CTF‐based flow‐cell electrolyzer exhibits a jCO of 201 mA cm−2 at −0.9 V with a high FECO of 98%. [ABSTRACT FROM AUTHOR]

Palladium has been proved to be an effective catalyst for CO2 electrocatalytic reduction. In this paper, nanostructured Pd particles fixed on polyaniline-covered MWNTs surfaces (Pd-PANI/CNT) were synthesized using an in situ method by reducing H2PdCl4 in a mixture of MWNTs and aniline with sodium citrate as protective stabilizer. TEM micrographs indicate that the addition of sodium citrate optimizes the size and distribution of the nanoparticles. In a 3-electrode system, both catalysts exhibit efficient and sustainable CO2 conversion towards formate but the one with sodium citrate addition is even better. The highest faradaic efficiency happens at −0.8 V vs. SCE and can be as high as 83 %. Based on the experiments, we put forward a mechanism of Pd-catalyzed CO2 electroreduction in aqueous solution in which Pd forms a PdH x hybrid that is involved in the reduction process with Pd. [ABSTRACT FROM AUTHOR]

The production of syngas by traditional processes such as steam methane reforming is energetically intensive and produces a large amount of CO2 emissions. In contrast, the electrochemical CO2 reduction reaction (CO2RR) enables the carbon neutral production of syngas at ambient conditions. Among non‐precious metal catalysts, metal‐nitrogen‐carbon electrocatalysts are inexpensive and highly selective towards syngas production. This study examined the selectivity of mono‐ and bi‐metallic (M−N−C, M=Fe, Mo or FeMo) electrocatalysts towards syngas production. The ratio of the CO : H2 in the syngas was tuned by modifying the ratio of the metallic precursors in the bi‐metallic FeMo−N−C catalysts, tailoring the catalysts' selectivity towards the CO2RR or the hydrogen evolution reaction (HER). The catalyst synthesis temperature(s) were considered as they influence the catalyst morphology and activity. Further, the dependence of the ratio of CO : H2 in the syngas as a function of the potential was explored for the different bi‐metallic catalysts. This work showed that by tailoring both the ratio of Fe : Mo in the bi‐metallic catalyst and optimizing the reductive potential, a CO : H2 ratio between 0.25 to 5 was achievable. This study demonstrated a novel approach in which the ratio of the product syngas composition could be tailored in a single reaction, without the need for further downstream processing to reach a desired composition. [ABSTRACT FROM AUTHOR]

A novel method for constructing a g‐C3N4/SnO2 heterostructure for CO2 reduction reaction (CO2RR) is presented. In the heterostructure, the introduction of g‐C3N4 makes for restraining the recombination of photo‐induced electrons and holes while the existence of SnO2 plays a vital role in selective catalytic reduction of CO2 into HCOOH, thus their cooperative interaction makes the photoelectric property of g‐C3N4/SnO2 towards CO2RR improved greatly. The so‐fabricated g‐C3N4/SnO2 shows an exclusive HCOOH selectivity and a high faradic efficiency of 58 %, which is about 8 times higher than that of single SnO2. The photocurrent reaches 7.5 μA cm−2 under 0.5 V. Besides, the overpotential is as low as 300 mV (vs. RHE). Moreover, the PL emission decreases obviously after the introduction of g‐C3N4. Given these performance advantages of g‐C3N4/SnO2, the solution‐processed strategy with post‐annealing treatment offers a facile, efficient, yet scalable approach reference to construct CO2RR heterostructure catalysts, which shows higher potential in CO2RR electrocatalysis. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of CO2 has been recognized as one of the best strategies to reduce atmospheric CO2 levels and achieve a carbon‐neutral economy. We report here a copper complex, Cu(salan)2, as an efficient CO2 reduction catalyst in basic aqueous media. Cu(salan)2 exhibited different catalytic behaviors in nanocrystalline and graphene‐supported forms. As nanocrystals, the complex did not show high catalytic activity and gradually decomposed into Cu2O upon electrolysis. However, when dispersed on a graphene matrix, Cu(salan)2 exhibited a moderate‐to‐high CO selectivity and remained stable in long‐term electrolysis. This work shows that site‐isolation by dispersion of a molecular catalyst is an effective way to increase the catalyst stability and tune the product selectivity for CO2RR electrocatalysis. [ABSTRACT FROM AUTHOR]

The chemical transformation of carbon dioxide (CO2) has been considered as a promising strategy to utilize and further upgrade it to value‐added chemicals, aiming at alleviating global warming. In this regard, sustainable driving forces (i.e., electricity and sunlight) have been introduced to convert CO2 into various chemical feedstocks. Electrocatalytic CO2 reduction reaction (CO2RR) can generate carbonaceous molecules (e.g., formate, CO, hydrocarbons, and alcohols) via multiple‐electron transfer. With the assistance of extra light energy, photoelectrocatalysis effectively improve the kinetics of CO2 conversion, which not only decreases the overpotentials for CO2RR but also enhances the lifespan of photo‐induced carriers for the consecutive catalytic process. Recently, rational‐designed catalysts and advanced characterization techniques have emerged in these fields, which make CO2‐to‐chemicals conversion in a clean and highly‐efficient manner. Herein, this review timely and thoroughly discusses the recent advancements in the practical conversion of CO2 through electro‐ and photoelectrocatalytic technologies in the past 5 years. Furthermore, the recent studies of operando analysis and theoretical calculations are highlighted to gain systematic insights into CO2RR. Finally, the challenges and perspectives in the fields of CO2 (photo)electrocatalysis are outlined for their further development. [ABSTRACT FROM AUTHOR]

In this work, a novel molecular device was assembled with cyanocobalamin (CNCbl)‐MWCNT/CP as an electrode for CO2 reduction coupled to water oxidation. In the half cell of water oxidation, the electrode displayed a stable current density of more than 10 h, showing excellent electrocatalytic stability of CNCbl‐MWCNT/CP. For only CO2 reduction, the electrode displayed a turnover number (TONCO) and turnover frequency (TOFCO) of 295390 and 8.2 s−1, respectively, and excellent Faradaic efficiency (FECO) of 96 % at −1.0 V vs. RHE. When using (CNCbl)‐MWCNT/CP as a bifunctional electrode in a full‐cell system for 3 h at 2.7 V, the gas products were 63.89 μmol of CO, 2.42 μmol of H2, and 26.93 μmol of O2, showing a high FECO of ca. 92 %. The unique structural advantages of CNCbl could improve electrocatalytic CO2 reduction and water oxidation. [ABSTRACT FROM AUTHOR]

Copper (Cu)-based materials for efficient CO2 conversion to adjustable syngas are reported. We employ an energy-efficient microwave-assisted route to synthesize copper/copper oxides with different structures and morphologies. The initial oxidation state of the copper on the surface significantly influences the performance of the materials in the CO2 reduction reaction (CO2RR). On the as-prepared material surface, a high content of Cu2O improves the selectivity toward CO and consequently the catalyzed CO2RR produce a syngas with a low H2/CO ratio, while the CuO performs poorly. In particular, Cu2O particles with a cubic shape show the highest selectivity for the CO formation. The superior catalytic activity of the Cu2O cubes for the CO2RR is attributed to the surface roughening under potential, which offers abundant electrochemically active sites and facilitates mass transport. [ABSTRACT FROM AUTHOR]

Abstract: Electrocatalytic reduction of CO2 to CO was achieved by using nitrogen‐doped Ta2O5, and the faradaic efficiency of CO reached 87.5 % at −0.73 V vs. RHE, whereas undoped Ta2O5 or “fully doped” Ta3N5 only yields H2. Nitrogen‐doped Ta2O5 was also a catalyst for photoassisted electrocatalytic CO2 reduction, and the total light‐to‐chemical efficiency reached 2.73 %. [ABSTRACT FROM AUTHOR]

Abstract: Electrocatalytic reduction of CO2 to CO was achieved by using nitrogen‐doped Ta2O5, and the faradaic efficiency of CO reached 87.5 % at −0.73 V vs. RHE, whereas undoped Ta2O5 or “fully doped” Ta3N5 only yields H2. Nitrogen‐doped Ta2O5 was also a catalyst for photoassisted electrocatalytic CO2 reduction, and the total light‐to‐chemical efficiency reached 2.73 %. [ABSTRACT FROM AUTHOR]

This work describes the electrochemical reduction of carbon dioxide in aqueous solution mediated by tetraruthenated metalloporphyrins (TRP; Co(II) and Zn(II)) in Nafion (Nf) and polyvinyl chloride (PVC) as a support. The comparative aspects of the two polymeric matrices are expressed in terms of the electrocatalytic behavior toward carbon dioxide reduction of both sets of modified electrodes; values of overpotential and turnover frequency were calculated in each case. The modified electrodes under survey were able to reduce carbon dioxide at −600 mV vs Ag/AgCl showing an enhanced reduction current and a decrease in the required overpotential compared to a bare glassy carbon (GC) electrode. Potential-controlled electrolysis experiments were carried out at −1000 mV in order to compare the distribution of products. The production of formic acid, formaldehyde and methanol was confirmed at potentials where reduction of solvent may occur. Measurements of electrochemical impedance spectroscopy show the presence of one active site for GC/Nf/MTRP (where M=Zn(II) and Co(II)) and three for GC/PVC/MTRP. This information corroborates the high values of TOF obtained for GC/PVC/ZnTRP as the best electrocatalyst. [ABSTRACT FROM AUTHOR]

Nickel/iron (Ni−Fe)-based compounds are known as active electrocatalysts for the oxygen evolution reaction (OER), which plays an important role in metal−air batteries and water splitting. Herein, a three-dimensional (3D) porous nickel foam electrode (NiFe(OH) x NSs/Nif) modified with Ni−Fe hydroxide nanosheets (NSs) is prepared by using a fast and facile electrodeposition method. The electrode is subsequently applied in the electrolysis of Na2CO3/NaHCO3 to produce hydrogen, oxygen, NaOH, and NaHCO3/CO2. By carefully controlling the electrodeposition time, ultrathin NiFe(OH) x NSs with a thickness of approximately 2-6 nm are interlaced with one another and grown vertically on nickel foam to form a hierarchical composite electrode. The prepared NiFe(OH) x NSs/Nif electrode exhibits superb OER performance with an overpotential of 260 mV at 10 mA cm−2 and a low Tafel slope of 29 mV dec−1 in 1 mol L−1 NaOH solution. In 0.5 mol L−1 Na2CO3/NaHCO3 solution, the NiFe(OH) x NSs/Nif electrode exhibits a low OER potential of 290 mV, which is lower than the commercial RuO2/Ti electrode at a current density of 100 mA cm−2, and shows good long-term stability. During electrolysis of Na2CO3/NaHCO3, the cell voltage with the NiFe(OH) x NSs/Nif anode is 2.52 V, which is 280 mV lower than that with a commercial RuO2/Ti anode. [ABSTRACT FROM AUTHOR]