![]() In addition, CO* is more stable on TMDC nanoflakes. COOH* formation is exergonic on metallic edges of TMDC nanoflakes rather than endergonic on metal surfaces, such as Ag, Pd, Au, and Cu. Therefore WSe 2 is the best TMDC for eCO 2RR and exhibit a TOF of 0.28 s −1 at an overpotential of 54 mV with 90% CO selectivity. This trend also correlates with the current density measurements of the four TMDCs, indicating the significance of electron transport in eCO 2RR. Theoretical calculations and experimental measurements of work functions of different TMDCs agree on a trend of MoS 2 > WS 2 > MoSe 2 > WSe 2. An aqueous solution of EMIM-BF 4, which was proven to promote CO 2 reactivity via complexation, was used as electrolyte for the electrochemical cell. With a chemical vapor transport technique, nanoflakes of MoS 2, WS 2, MoSe 2, and WSe 2 were fabricated. reported a high eCO 2RR performance using 2D nanoflakes of different TMDCs in an ionic liquid of 3-methylimidazolium tetrafluoroborate (EMIM-BF 4). ![]() Since WSe 2, WS 2, MoSe 2, and MoS 2 share similar structures, their eCO 2RR catalytic properties are often investigated and compared with each other. Copyright 2016, American Association for the Advancement of Science. Reproduced with permission from reference Y. CO 2, H xC yO z and CO are isolated molecules, while the bonded species are adsorbed intermediates. Proposed reaction mechanism of CO 2 reduced to CO on MoS 2 edges. The fluorosilane accelerates CO 2 diffusion by providing a three-phase contact point and suppresses HER by its hydrophobicity.įigure 8.6. functionalized exfoliated MoS 2 nanosheets with fluorosilane and obtained efficient syngas production with a tunable CO/H 2 ratio. ![]() The outstanding catalytic performance was attributed to the large quantity of active sites granted by the hollow architecture and electron transfer from N-doped carbon to MoS 2 edges. With this catalyst, a current density of 34.31 mA cm −2 with FE CO of 92.68% at an overpotential of 590 mV was achieved. MoO xS y was coated onto ZIF-67 crystallite template, and during the following pyrolysis step, the core–shell composite was converted into MoS 2 and N-doped carbon, respectively ( Fig. fabricated a hollow composite of MoS 2 and N-doped carbon. RHE), and the catalyst is stable over 1000 cycles with a FE CO of 85%. The HER is effectively suppressed when increasing potential from −0.21 to −0.70 V (vs. After validating the presence of Ti-S bonds formed at the interface of TiO 2 and MoS 2, theoretical calculations proved that such composite structures decrease both the binding energy of CO 2 and the energy barriers of eCO 2RR. MoS 2 was formed inside TiO 2 nanosheet scaffolds via hydrothermal synthesis and calcination ( Fig. designed a 3D TiO 2 architecture for selective reduction of CO 2 to CO. While other works focus on manipulating the intrinsic atomic structure, TMDCs can also be incorporated in composites to improve the performance. These two effects result in an optimized Nb concentration of 5% for best performance. Moreover, further doping will enlarge the work function and hinder electron transport. The turnover frequency (TOF) of Mo 0.95Nb 0.05S 2 is one order of magnitude higher than undoped MoS 2, because Nb atoms can promote the desorption of CO. The same group later reported that Nb-doped MoS 2 nanosheets exhibit even higher current density. ![]() A FE CO of 98% with a current density of 130 mA cm −2 at an overpotential of 54 mV was achieved. They fabricated vertically aligned MoS 2 nanosheets as electrocatalysts, with the edges ended with Mo atoms. In addition, the reduced overpotential and reaction barrier of eCO 2RR are attributed to the synergistic mechanism of electrolyte ions and edge Mo atoms. Theoretical calculations including projected density of states (PDOS) and DFT revealed that, at Mo terminated edges, a narrowed energy gap between d-band and Fermi energy level, together with an excess of d-electrons, contribute to the high current density. demonstrated that MoS 2 nanosheets exhibit remarkably high eCO 2RR efficiency and current density. To tackle this challenge, defects, edge sites, and dopants of electrocatalysts should be carefully designed. Since HER is a competitive reaction to eCO 2RR, how to suppress HER has become a key challenge to increase eCO 2RR efficiency of MoS 2. Among TMDCs, MoS 2 first appears to be an efficient catalyst for HER because S atoms often function as strong bonding sites to H +. TMDCs possess a two-dimensional lattice structure where metal and chalcogen atoms are aligned hexagonally. Transition metal dichalcogenides (TMDCs) are also considered as a cost-effective and nontoxic substitute for noble metal catalysts for eCO 2RR. Zhicheng Zhang, in Nanomaterials for CO2 Capture, Storage, Conversion and Utilization, 2021 8.2.3 2D metal chalcogenides
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