The precious metal-based catalyst is of great significance in the chemistry industry. Compared to non-precious metal-based catalysts, precious metal-based catalysts possess irreplaceable catalytic activity, good selectivity, use safety, and stability, thus making them the most important material in both conventional thermal catalytic reactions and electrochemical catalytic reactions including electrochemical CO2reduction (CO2RR), NO3- reduction reaction(NO3RR), and water splitting. In the past few years, we develop several kinds of precious metal-based catalysts for CO2RR and they show very good performance in both aqueous CO2RR and Li-CO2 batteries.
For electrocatalytic CO2RR, precious metals, such as Ag, Au, and Pd are excellent catalysts with acceptable CO activity and selectivity in an aqueous system. And many different methods are used to further improve their performance.[1][2] Unusual phase metal nanomaterials usually possess much higher intrinsic catalytic activity than their conventional phase.[3] By rational design and careful preparation, we prepared a series of metal-based catalysis with an unconventional phase. And for the first time, we report the surface molecular functionalization of unusual phase 4H/facecentered cubic (fcc) Au nanorods with 5-mercapto-1-methyltetrazole (MMT) for high-performance electrochemical CO2RR under industry-relevant current density, as shown in Figure 1. [4] The MMT-modified 4H/fcc Au nanorods (denoted as 4H/fcc Au-MMT) demonstrate significantly enhanced CO2RR performance than the initial oleylamine (OAm)-capped 4H/fcc Au nanorods (denoted as 4H/fcc Au-OAm) in both H-type cell and flow cell under a wide range of potentials and current densities. Significantly, MMT-modified 4H/ fcc Au nanorods deliver an excellent carbon monoxide selectivity of 95.6% under the industry-relevant current density of 200 mA cm−2. In addition, surface molecular functionalization of 4H/fcc Au nanorods with a family of MMT derivatives can also remarkably increase the CO2RR performance. And this facile surface molecular functionalization method can also be extended to the conventional fcc Au nanomaterials.
Ru, Ir and Rh are effective catalysts for CO2RR in Li-CO2 batteries. LiCO2 batteries have been regarded as a promising candidate for the next-generation high-performance energy conversion and storage techniques with carbon-neutral capability. It can not only reduce the CO2 into C but also provide energy for specific applications. By rational design and careful preparation, we developed a versatile method for the controllable synthesis of ultrathin 2D Ru-M (M = Co, Ni, and Cu) nanosheets (NSs) as the cathode catalysts for aprotic Li-CO2 batteries, which effectively decrease the charge voltage and overpotential, as shown in Figure 2.[5] Impressively, the charge voltage and corresponding overpotential for RuCo NSs are 3.74 V and 0.94 V, respectively, which are much lower than those of RuCo nanoparticles and bare carbon nanotubes, and also superior over most of the reported metal and metal-based catalysts for LiCO2 batteries so far. Ex/in situ experimental studies and theoretical investigations suggest that RuCo NSs can facilitate the round-trip CO2RR and CO2ER kinetics through the promoted adsorption toward Li and CO2 and also the enhanced electron interaction with Li2CO3 by in-plane RuCo alloy active sites, respectively.
Figure 1 Preparation method and structural characterization of 4H/fcc Au-MMT.
In addition, these kinds of precious metals can also be used to tune the selectivity of Cu-based catalysts via forming tandem catalysts or heterostructures, especially for the production of value-added multicarbon products (C2+). Generally, Ag, Au, and Pd are COselectivity catalysts, and Cu can reduce CO to multi-carbon products more easily. A Tandem catalyst combining precious metals with Cu can decrease the CO2RR energy barrier and improve the activity and selectivity of C2+. Thus, via the rational control of surfactant and reduction kinetics of Cu precursor, we synthesize three kinds of Ag– Cu Janus nanostructures with {100} facets (JNS-100), as shown in Figure 3.[6]These Ag–Cu JNS-100 are all highly selective tandem catalysts for the electrochemical reduction of CO2 to C2+ products. Impressively, the Cu nanoparticles are grown along one side of the silver nanocubes, which is the first reported cube-to-cube Junus structure. Significantly, Cu(100) facet is beneficial for the production of C2+ products, so the novel Janus structure shows very good CO2RR performance toward C2+ products. In particular, Ag65–Cu35 JNS-100 can effectively achieve excellent faradaic efficiency of 54% and 72% for C2H4 and C2+ products, respectively.
In summary, we realized the controlled synthesis of unconventional phase Au-based catalysts, Ru-M ultrathin nanosheet, and Ag-Cu cube-to-cube Junus structure for CO2 reduction. Phase engineering of precious metals will not only enrich the catalysts for CO2RR and beyond but also inspire new theories in material science and catalysis science.[7][8] And the rational design of hetero nanostructures with the integration of two or more materials are one of the most effective ways to improve their performance, which will contribute to the development of structure control and interface engineering. And the innovation in materials will finally contribute to the practical application in chemistry and beyond.
Figure 2 Synthetic route and structural characterization of ultrathin RuCo alloy nanosheets for the aprotic LiCO2 battery.
Figure 3 Synthetic protocol and structural characterization of Ag–Cu JNS-100.
Reference
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