Adv. Funct. Mater.: Wang Xiaohui, Institute of Metal Research, Chinese Academy of Sciences: Ultra-stable MXene@Pt/SWCNTs nanocatalyst for hydrogen evolution reaction

【introduction】

Hydrogen (H2) has the advantage of clean energy, and its energy density is as high as 120-140 MJ kg−1. The hydrogen evolution reaction (HER) represents a highly efficient electrical conversion route. However, in the absence of a suitable catalyst, high overpotential often leads to low efficiency. Although people have made great efforts to find non-precious metal catalysts that are inexpensive and can be used for HER, unfortunately, since the free energy change value of the instantaneous adsorption of H* on the Pt surface is almost zero, no catalyst can win Too low overpotential and fast kinetic Pt. Considering the low abundance of Pt on the earth, the construction of heterogeneous Pt-based nanocatalysts has become a trend to maximize activity and durability while minimizing the use of Pt resources. Because nano/atom Pt has good conductivity and chemical stability, it often uses carbon-based materials as carriers (from carbon materials with good conductivity and chemical stability, it is often used as a carrier for nano-atom Pt). These carbon-based materials Including but not limited to carbon black, graphene, porous carbon, etc. However, these chemically inert carbon-based materials cannot reduce Pt cations by wet chemical methods, which requires additional reducing agents or complicated post-treatment processes to prepare Pt/C electrocatalysts. Recently, a new 2D material MXenes has been discovered, which has been determined to have high conductivity, hydrophilicity and reducibility. First-principles calculations and experimental results show that the low work function of Ti3C2Tx MXene enables spontaneous reduction of precious metal cations into metal nanoparticles without the need for additional reducing agents or post-treatment. In addition to high activity, electrocatalysts based on Pt group metals must have long-term durability before they can be used in practical applications. Pt-based metals used for HER are usually fixed on the surface of the carrier using a polymer binder (such as Nafion). However, these insulating polymer binders block active sites, inhibit ion diffusion, and increase electron transfer resistance. Single-walled carbon nanotubes (SWCNTs) have excellent conductivity, but are rarely used as conductive binders for HER catalysts.

【Achievement Introduction】

Recently, under the leadership of the team of Wang Xiaohui, a researcher from the Institute of Metal Research, Chinese Academy of Sciences (corresponding author), in cooperation with the Lawrence Berkeley National Laboratory and Zhengzhou University in the United States, a stratification for the HER catalyst was proposed (it is recommended to change to multi-level, the same below) ) Pt-MXene-SWCNTs heterostructure scheme. In the heterostructure, the highly active nano/atomic metal Pt is fixed on the Ti3C2Tx MXene sheet (MXene@Pt) and is connected to a network of conductive SWCNTs. By filtering the mixed colloidal suspension containing MXene@Pt and SWCNTs, a layered heterogeneous structure was constructed. Taking advantage of the hydrophilicity and reducibility of MXene, the MXene@Pt colloidal suspension is prepared by spontaneously reducing Pt cations to metallic Pt without the need for additional reducing agents or post-treatment. The film-like layered HER catalyst prepared in this way showed high stability during 800 hours of operation, and its capacity current density was as high as 230 mA cm-3 at -10 mA cm-2 under -50 mV vs. RHE Under the current density, its overpotential is as low as -62 mV vs. RHE. This solution provides a simple, efficient and scalable method to construct a stable and efficient HER catalyst. Considering the nature and structure-activity relationship of layered Pt-MXene-SWCNTs heterostructures, other MXenes may show greater potential in HER electrocatalysis. Related achievements were published on Adv. Funct. Mater. entitled "Ultrastable MXene@Pt/SWCNTs‘ Nanocatalysts for Hydrogen Evolution Reaction".

【Graphic introduction】

Figure 1 Schematic diagram of preparation of Ti3C2Tx MXene colloidal suspension and MXene@Pt/SWCNTs nanocatalyst

a) Schematic diagram of preparation of Ti3C2Tx MXene colloidal suspension.

b) Schematic diagram of preparation of MXene@Pt/SWCNTs nanocatalyst.

Figure 2 Characterization and element analysis

a) TEM image of several layers of submicron Ti3C2Tx nanoflakes.

b) TEM image of Ti3C2Tx@5Pt.

c) HAADF-STEM image of MXene @5Pt.

d) Distribution map of corresponding elements of Ti, C, Pt and O.

e) Atomic HAADF-STEM image of Ti3C2Tx@5Pt.

f) The particle size distribution of Pt nanoparticles.

g) A single Pt atom was observed on Ti3C2Tx@5Pt.

h) TEM image of SWCNTs after tip-probe ultrasound treatment.

i) SEM image of SWCNTs film.

Figure 3 High and low power SEM characterization of the film

a) High magnification SEM images of S-M, c) S-M-1Pt and e) S-M-5Pt.

b) Low magnification SEM images of S-M, d) S-M-1Pt and f) S-M-5Pt.

Figure 4 XPS analysis of prepared samples

a) Spectrograms of Ti3C2Tx, Ti3C2Tx@1Pt and Ti3C2Tx@5Pt.

b-d) b) Ti3C2Tx, c) Ti3C2Tx@1Pt and d) Ti3C2Tx@5Pt in the Ti2p area.

e) Pt 4f peaks of Ti3C2Tx@1Pt and Ti3C2Tx@5Pt. The binding energy of Pt 4f is located at 72.0 and 75.3 eV, and moves in a direction higher than Pt0.

Figure 5 HER catalytic performance of the prepared catalyst

a) Polarization curve of current density and potential.

b) Polarization curve of volume current and potential.

c) Tafel curve of the prepared catalyst.

d) LSV curve of multilayer S-M-5Pt.

e) Long-term operating stability of five S-M-5Pt operating at a current density of -10 mA cm-2 for 800 h.

Figure 6 Kinetic study of the prepared catalyst

a-e) EIS spectra of a) SWCNTs, b) S-M, d) S-M-1Pt and e) S-M-5Pt at -50 mV vs. Ag/AgCl and vs. RHE potentials

c) Equivalent circuit diagram of pseudocapacitor behavior

f) Equivalent circuit diagram of HER behavior. In the absence of Pt, S-M exhibits pseudocapacitive behavior, while in the presence of Pt substance at -50 mV vs. RHE, S-M-1Pt and S-M-5Pt exhibit HER behavior.

【summary】

In summary, using the special characteristics of Ti3C2Tx MXene to maintain its physicochemical properties after reducing platinum complex ions and SWCNTs as a conductive binder, a layered Pt-MXene-CNTs heterostructure was constructed as a high-performance HER catalyst. The layered HER catalyst prepared in the form of a thin film exhibits very high stability during 800 hours of operation. At -50 mV vs. RHE, its high-capacity current density can reach 230 mA cm-3 at -10 At mA cm-2, the low overpotential is -62 mV vs. RHE. The solution treatment method used in this study provides a simple, efficient and scalable strategy for the construction of nano/atomic precious metal immobilized (anchored on MXene) catalysts on MXene, and SWCNTs also act as binders And collectors. This method not only provides a strategy for the synthesis of Pt-based catalysts, but also paves the way for further exploration and design of high-efficiency catalysts or sensors based on precious metal immobilization (anchoring) MXene/CNT composites.

Literature link: Ultrastable MXene@Pt/SWCNTs‘ Nanocatalysts for Hydrogen Evolution Reaction (Adv. Funct. Mater., 2019, DOI: 10.1002/adfm.202000693)

This article was translated by Mu Wentao, edited and edited by Niu.

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