Search

Electrochemical carbon dioxide reduction (ECO 2 RR) shows great potential to create high-value carbon-based chemicals, while designing advanced catalysts at the atomic level remains challenging. The ECO 2 RR performance is largely dependent on the catalyst microelectronic structure that can be effectively modulated through surface defect engineering. Here, we provide an atmosphere-assisted low-temperature calcination strategy to prepare a series of single-atomic Cu/ceria catalysts with varied oxygen vacancy concentrations for robust electrolytic reduction of CO 2 to methane. The obtained Cu/ceria catalyst under H 2 environment (Cu/ceria-H 2 ) exhibits a methane Faraday efficiency (FE CH4 ) of 70.03 % with a turnover frequency (TOF CH4 ) of 9946.7 h -1 at an industrial-scale current density of 150 mA cm -2 in a flow cell. Detailed studies indicate the copious oxygen vacancies in the Cu/ceria-H 2 are conducive to regulating the surface microelectronic structure with stabilized Cu + active center. Furthermore, density functional theory calculations and operando ATR-SEIRAS demonstrate that the Cu/ceria-H 2 can markedly enhance the activation of CO 2 , facilitate the adsorption of pivotal intermediates *COOH and *CO, thus ultimately enabling the high selectivity for CH 4 production. This study presents deep insights into designing effective electrocatalysts for CO 2 to CH 4 conversion by controlling the surface microstructure via the reaction atmosphere., (© 2024 Wiley-VCH GmbH.)

Copper (Cu) nanomaterials are a unique kind of electrocatalysts for high-value multi-carbon production in carbon dioxide reduction reaction (CO 2 RR), which holds enormous potential in attaining carbon neutrality. However, phase engineering of Cu nanomaterials remains challenging, especially for the construction of unconventional phase Cu-based asymmetric heteronanostructures. Here the site-selective growth of Cu on unusual phase gold (Au) nanorods, obtaining three kinds of heterophase fcc-2H-fcc Au-Cu heteronanostructures is reported. Significantly, the resultant fcc-2H-fcc Au-Cu Janus nanostructures (JNSs) break the symmetric growth mode of Cu on Au. In electrocatalytic CO 2 RR, the fcc-2H-fcc Au-Cu JNSs exhibit excellent performance in both H-type and flow cells, with Faradaic efficiencies of 55.5% and 84.3% for ethylene and multi-carbon products, respectively. In situ characterizations and theoretical calculations reveal the co-exposure of 2H-Au and 2H-Cu domains in Au-Cu JNSs diversifies the CO* adsorption configurations and promotes the CO* spillover and subsequent C-C coupling toward ethylene generation with reduced energy barriers., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

Precise regulation of the active site structure is an important means to enhance the activity and selectivity of catalysts in CO 2 electroreduction. Here, we creatively introduce anionic groups, which can not only stabilize metal sites with strong coordination ability but also have rich interactions with protons at active sites to modify the electronic structure and proton transfer process of catalysts. This strategy helps to convert CO 2 into fuel chemicals at low overpotentials. As a typical example, a composite catalyst, CuO/Cu-NSO 4 /CN, with highly dispersed Cu(II)-SO 4 sites has been reported, in which CO 2 electroreduction to formate occurs at a low overpotential with a high Faradaic efficiency (-0.5 V vs. RHE, FE formate =87.4 %). Pure HCOOH is produced with an energy conversion efficiency of 44.3 % at a cell voltage of 2.8 V. Theoretical modeling demonstrates that sulfate promotes CO 2 transformation into a carboxyl intermediate followed by HCOOH generation, whose mechanism is significantly different from that of the traditional process via a formate intermediate for HCOOH production., (© 2024 Wiley-VCH GmbH.)

Precious-metal single-atom catalysts (SACs), featured by high metal utilization and unique coordination structure for catalysis, demonstrate distinctive performances in the fields of heterogeneous and electrochemical catalysis. Herein, gold SACs are constructed on hierarchical nitrogen-doped carbon nanocages (hNCNC) via a simple impregnation-drying process and first exploited for electrocatalytic carbon dioxide reduction reaction (CO 2 RR) to produce syngas. The as-constructed Au SAC exhibits the high mass activity of 3319 A g -1 Au at -1.0 V (vs reversible hydrogen electrode, RHE), much superior to the Au nanoparticles supported on hNCNC. The ratio of H 2 /CO can be conveniently regulated in the range of 0.4-2.2 by changing the applied potential. Theoretical study indicates such a potential-dependent H 2 /CO ratio is attributed to the different responses of HER and CO 2 RR on Au single-atom sites coordinating with one N atom at the edges of micropores across the nanocage shells. The catalytic mechanism of the Au active sites is associated with the smooth switch between twofold and fourfold coordination during CO 2 RR, which much decreases the free energy changes of the rate-determining steps and promotes the reaction activity., (© 2023 Wiley‐VCH GmbH.)

CO 2 electrolysis in acid has emerged as a promising route to achieve high CO 2 utilization due to the inhibition of undesired carbonate formation that generally occurs in alkaline or neutral conditions. However, the efficiency and stability of this system need to be further improved through tailoring of the electrocatalyst and its working environment. Here, a working microenvironment of structurally engineered NiNC catalyst for acidic CO 2 electrolysis is probed and optimized by adding hydrophobic poly(tetrafluoroethylene) (PTFE) nanoparticles in the catalytic layer of gas-diffusion electrodes. The PTFE-modified electrode delivers nearly 100% CO Faradaic efficiency at an industry-relevant current density of 250 mA cm -2 , and a high single-pass CO 2 utilization of 75.7% at a current density of 200 mA cm -2 under 20 sccm CO 2 gas flow rate. Moreover, compared to a conventional electrode without added PTFE, the PTFE-modified electrode exhibits a substantially enhanced water-flooding-resistant ability. Mechanistic investigations reveal that a moderate PTFE modification can optimize the local CO 2 /H 2 O ratio in the catalytic layer, favoring the reduction of the diffusion layer thickness and the formation of a highly active and stable solid-liquid-gas interfacial microenvironment., (© 2022 Wiley-VCH GmbH.)

Reaction temperature is an important parameter to tune the selectivity and activity of electrochemical CO 2 reduction reaction (CO 2 RR) due to different thermodynamics of CO 2 RR and competitive hydrogen evolution reaction (HER). In this work, temperature-dependent CO 2 RR over Fe-N-C and Ni-N-C single-atom catalysts are investigated from 303 to 343 K. Increasing the reaction temperature improves and decreases CO Faradaic efficiency over Fe-N-C and Ni-N-C catalysts at high overpotentials, respectively. CO current density over Fe-N-C catalyst increases with temperature, then gets into a plateau at 323 K, finally reaches the maximum value of 185.8 mA cm -2 at 343 K. While CO current density over Ni-N-C catalyst achieves the maximum value of 252.5 mA cm -2 at 323 K, and then drops significantly to 202.9 mA cm -2 at 343 K. Temperature programmed desorption results and density functional theory calculations reveal that the difference of temperature-dependent variation on CO Faradaic efficiency and current density between Fe-N-C and Ni-N-C catalysts results from the varied adsorption strength of key reaction intermediates during CO 2 RR., (© 2021 Wiley-VCH GmbH.)

Electrochemical energy storage and conversion is an effective strategy to relieve the increasing energy and environment crisis. The sluggish reaction kinetics in the related devices is one of the major obstacles for them to realize practical applications. More efforts should be devoted to searching for high-efficiency electrocatalysts and enhancing the electrocatalytic performance. 3D graphene macrostructures (3D GMs) are one kind of porous crystalline materials with 3D structures at both micro- and macro-scale. The unique structure can achieve large accessible surface area, expose many active sites, promote fast mass/electron transport, and provide wide room for further functional modification. All these features make them promising candidates for electrocatalysis. In this review, the authors focus on the latest progress of 3D GMs for electrocatalysis. First, the preparation methods of 3D GMs are introduced followed by the strategies for functional modifications. Then, their electrocatalytic performances are discussed in detail including monofunctional and bifunctional electrocatalysis. The electrocatalytic processes involve oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and carbon dioxide reduction reaction. Finally, the challenges and perspectives are presented to offer a guideline for the exploration of excellent 3D GM-based electrocatalysts., (© 2021 Wiley-VCH GmbH.)

Developing copper-free catalysts for CO 2 conversion into hydrocarbons and oxygenates is highly desirable for electrochemical CO 2 reduction reaction (CO 2 RR). Herein, we report a cobalt phthalocyanine (CoPc) and zinc-nitrogen-carbon (Zn-N-C) tandem catalyst for CO 2 RR to CH 4 . This tandem catalyst shows a more than 100 times enhancement of the CH 4 /CO production rate ratio compared with CoPc or Zn-N-C alone. Density functional theory (DFT) calculations and electrochemical CO reduction reaction results suggest that CO 2 is first reduced into CO over CoPc and then CO diffuses onto Zn-N-C for further conversion into CH 4 over Zn-N 4 site, decoupling complicated CO 2 RR pathway on single active site into a two-step tandem reaction. Moreover, mechanistic analysis indicates that CoPc not only generates CO but also enhances the availability of *H over adjacent N sites in Zn-N 4 , which is the key to achieve the high CH 4 production rate and understand the intriguing electrocatalytic behavior which is distinctive to copper-based tandem catalysts., (© 2020 Wiley-VCH GmbH.)

Simultaneously achieving high Faradaic efficiency, current density, and stability at low overpotentials is essential for industrial applications of electrochemical CO 2 reduction reaction (CO 2 RR). However, great challenges still remain in this catalytic process. Herein, a synergistic catalysis strategy is presented to improve CO 2 RR performance by anchoring Fe-N sites with cobalt phthalocyanine (denoted as CoPc©Fe-N-C). The potential window of CO Faradaic efficiency above 90% is significantly broadened from 0.18 V over Fe-N-C alone to 0.71 V over CoPc©Fe-N-C while the onset potential of CO 2 RR over both catalysts is as low as -0.13 V versus reversible hydrogen electrode. What is more, the maximum CO current density is increased ten times with significantly enhanced stability. Density functional theory calculations suggest that anchored cobalt phthalocyanine promotes the CO desorption and suppresses the competitive hydrogen evolution reaction over Fe-N sites, while the *COOH formation remains almost unchanged, thus demonstrating unprecedented synergistic effect toward CO 2 RR., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The electroreduction of carbon dioxide (CO 2 ) toward high-value fuels can reduce the carbon footprint and store intermittent renewable energy. The iodide-ion-assisted synthesis of porous copper (P-Cu) microspheres with a moderate coordination number of 7.7, which is beneficial for the selective electroreduction of CO 2 into multicarbon (C 2+ ) chemicals is reported. P-Cu delivers a C 2+ Faradaic efficiency of 78 ± 1% at a potential of -1.1 V versus a reversible hydrogen electrode, which is 32% higher than that of the compact Cu counterpart and approaches the record (79%) reported in the same cell configuration. In addition, P-Cu shows good stability without performance loss throughout a continuous operation of 10 h., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Electrochemical reduction of CO 2 (ERC) to useful chemicals is an environmentally and technologically significant process. The process is confronted with significant challenges to simultaneously enhance the catalyst activity and product selectivity. In this paper, the effects of organic additives on the ERC process were systematically investigated by using DFT to screen additives with different functional groups for enhanced activity and selectivity. In particular, the additives with -NH 3 + and -SO 3 H groups had a remarkably positive effect on the ERC activity and hydrocarbon selectivity, which were predicted to impart a positive shift on onset potential of approximately 162 and 108 mV, respectively. Importantly, the additive can accelerate the electron transfer of the intermediate and tune the electronic structure of the catalyst surface, resulting in a clear deviation from transition-metal scaling lines. Combining bonding energy of crucial intermediates with partial atomic charge analysis, we rationalized the negative effect of high concentration additives and confirmed the proposed electron transfer model. Furthermore, additive molecules containing functional groups with positive charges and maximizing the deviation from transition-metal scaling lines are meaningful strategies to design and choose organic additives to enhance activity and selectivity of ERC., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

As synthetic methods advance for metal nanoparticles, more rigorous studies of structure-function relationships can be made. Many electrocatalytic processes depend on the size, shape, and composition of the nanocatalysts. Here, the properties and electrocatalytic behavior of random alloyed and intermetallic nanoparticles are compared. Beginning with an introduction of metallic nanoparticles for catalysis and the unique features of bimetallic compositions, the discussion transitions to case studies of nanoscale electrocatalysts where direct comparisons of alloy and intermetallic compositions are undertaken for methanol electrooxidation, formic acid electrooxidation, the oxygen reduction reaction, and the electroreduction of carbon dioxide (CO 2 ). Design and synthesis strategies for random alloyed and intermetallic nanoparticles are discussed, with an emphasis on Pt-M and Cu-M compositions as model systems. The differences in catalytic performance between alloys and intermetallic nanoparticles are highlighted in order to provide an outlook for future electrocatalyst design., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)