Nature sub-journal of Peng Shengjie's research group of Nanjing University of Aeronautics and Astronautics: Rapid and complete reconstruction induces real active components for quasi-industrial hydrogen evolution reaction [Article information] Rapid and complete reconstruction in

Nanjing University of Aeronautics and Astronautics Peng Shengjie Research Group Nature Sub-job: Rapid complete reconstruction induces real active components for quasi-industrial hydrogen evolution reaction

【Article information】

Rapid complete reconstruction induces real active components for quasi-industrial hydrogen evolution reaction

First author: Wang Luqi

Corresponding author: Peng Shengjie*

Unit: Nanjing University of Aeronautics and Astronautics

[Research background]

With the increasing attention to energy crisis and environmental pollution, people vigorously develop sustainable clean energy. hydrogen fuel has a high energy density and environmental friendliness. It is an excellent energy carrier, which helps to achieve the goal of carbon neutralization . Among various hydrogen production processes, it is a promising method for hydrogen production of electrolyzed water to produce hydrogen to obtain hydrogen gas with high purity and no exhaust gas carbon dioxide . As one of the semi-reactions of water cracking, hydrogen evolution reaction (HER) is an important factor affecting hydrogen production technology, which requires the development of high-efficiency hydrogen evolution catalysts with rapid kinetics. Reasonable modulation of electrochemical reconstruction and identification of the real source of activity are one of the important methods to optimize the performance of electrocatalysts.

Oxygen evolution reaction (OER) catalysts under electrochemical conditions usually undergo a surface reconstruction process to form highly active metal oxides or (oxygen) hydroxide , which has been proven to be the actual active phase. However, reconstitution processes that improve electrocatalytic activity rarely occur in HER catalysts. Only a few reports have shown that the catalyst exhibits nanoscale reconstruction near the surface during the HER process. This surface-shallow reconstruction, due to its slow reconstruction process and limited active surface area, the derived catalyst often exhibits incompletely developed catalytic activity, resulting in lower component utilization.

​In addition, the complex components of the surface reconstruction catalyst greatly hindered in-depth research on the origin of catalytic. Therefore, exploring the dynamic reconstruction mechanism of catalysts to induce rapid and complete reconstruction of catalysts and reveal actual catalytically active species is conducive to the accurate design of efficient HER electrocatalysts, but is still facing challenges.

[Article Introduction]

Recently, Professor Peng Shengjie's research team of Nanjing University of Aeronautics and Astronautics and others reasonably designed the hydrogen evolution reaction (HER) catalyst to induce its rapid and complete reconstruction, thereby producing highly active catalytic species. Specifically, a heterostructure catalyst (CoC2O4@MXene) that encapsulates CoC2O4 by MXene nanosheets was prepared using a self-assembly strategy. The CoC2O4@MXene catalyst with hollow nanotube structure shows high electron accessibility and abundant electrolyte diffusion channels, which is conducive to the implementation of a rapid and complete reconstruction process. This rapid complete reconstruction induces a transition from CoC2O4 to the actual catalytically active species Co(OH)2.

​ Studies show that the recombination of low-price defect-rich Co(OH)2 with MXene promotes rapid electron transfer and reduces the free energy of the Volmer step, thereby accelerating HER dynamics. The reconfigured components only require low overpotentials of 28 and 216 mV to reach current density of 10 and 1000 mA cm-2 under alkaline conditions. At the same time, good activity and stability are still maintained in the harsh natural seawater environment.

​This article is published in the top international journal Nature Communications under the title of Rapid Complete Reconfiguration Induced Actual Active Species for Industrial Hydrogen Evolution Reaction.

Figure 1. Induce rapid and complete transformation of CoC2O4@MXene during electrochemical HER.

[Key points of this article]

Key points 1: Rational design of precatalyst

Used an interface induction self-assembly strategy to synthesize CoC2O4@MXene precatalyst with hollow nanotube structure. tubular structure not only exhibits a high specific surface area, but also has rich diffusion channels to activate the diffusion dimension of the electrolyte and to remove the limitations of mass transportation.Even the electrolyte can enter the interior of the CoC2O4@MXene matrix, which provides a larger electrolyte-electrocatalyst interface. In addition, the introduction of highly hydrophilic MXene greatly improves water adsorption and electrode wetting, and this unique structure provides feasibility for spontaneous rapid complete reconstruction.

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Keypoint 2: Rapid complete reconstruction mechanism

Continuous LSV scans in 1 M KOH induced a sharp drop in the overpotential of CoC2O4@MXene. A stable polarization curve was achieved after only 5 cycles, which showed that CoC2O4@MXene has the characteristics of rapid reconstruction. In-situ Raman and HRTEM further reveal the complete reconstruction process from CoC2O4@MXene to Co(OH)2@MXene. In addition, the analysis results of XPS and XAS show that the in-situ reconstruction form Co(OH)2 has low-price defect-rich structural characteristics, which is very different from the Co(OH)2 prepared by classical methods.

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Key points three: Excellent catalytic activity of high current density

Electrochemical tests show that the overpotential of the reconstructed R-CoC2O4@MXene at 10 mA cm-2 current density is only 28 mV. In particular, R-CoC2O4@MXene catalysts exhibited a smaller overpotential of 157 and 216 mV at high current densities of 500 and 1000 mA cm-2, which is far superior to commercial Pt/C. Performance analysis at TOF and high current density further verified its superior HER intrinsic activity. In addition, R-CoC2O4@MXene can maintain stability for 100 h at current densities of 10, 500 and 1000 mA cm-2, indicating that the catalyst has potential industrial application value.

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Key points 4: Density general function theory calculation

In order to clarify the relationship between the electronic structure of R-CoC2O4@MXene and the excellent HER catalytic activity, the structural model was calculated in density functional theory (DFT). Defect-rich low-priced Co sites exhibit optimized Fermi level and significantly decreased D-band center. Differential charge density also reveals charge redistribution in R-CoC2O4@MXene. This behavior of charge redistribution can optimize the absorption energy of the reaction intermediate and thus improve catalytic activity. The favorable free energy of water adsorption (ΔEH2O) and hydrodissociation (ΔGH2O) at the unsaturated Co sites in the low-valent state effectively promotes the progress of the Volmer step. Furthermore, the hydrogen adsorption free energy (ΔGH*) close to the thermal median value indicates that there is a suitable reaction energy barrier for H* adsorption and H2 desorption at the Co sites that are unsaturated in the low-valent state. Overall, R-CoC2O4@MXene with unsaturated coordination metal Co sites optimizes the Gibbs free energy of the HER reaction and the electronic structure of the catalyst, thereby improving the catalytic performance.

[Conclusion]

To sum up, we cleverly designed a new CoC2O4@MXene tubular precatalyst with fast and complete reconstruction characteristics to improve HER performance. high electron accessibility and abundant electrolyte diffusion channels induced a rapid complete reconstruction process of CoC2O4@MXene, forming a Co(OH)2@MXene complex with low valence state and defect-rich. A large number of exposed low-priced Co sites provide available charge transfer orbits, facilitating the electron transport process. In situ characterization and DFT calculations show that the resulting Co(OH)2@MXene after reconstruction presents an adjusted electronic structure, which optimizes the reaction energy barrier between hydrolysis and H* intermediate adsorption and improves the intrinsic activity of HER reactions.

​The reconfigured Co(OH)2@MXene electrocatalyst thus exhibits excellent HER performance, with overpotentials as low as 28 and 216 mV at current density of 10 and 1000 mA cm-2, respectively. More importantly, the catalytic activity of Co(OH)2@MXene is stable in alkaline seawater and natural seawater, which is better than commercial Pt/C. Our research provides an in-situ reconstruction of electrocatalysts during the HER process and promotes the rational design and controllable preparation of high-performance catalysts for sustainable hydrogen production.

[Article link]

Rapid complete reconfiguration induced actual active species for industrial hydrogen evolution reaction

https://doi.org/10.1038/s41467-022-33590-5

[ Introduction to the corresponding author ]