Background
Hydrogen, as a clean and renewable energy source, is considered a promising energy candidate to replace fossil fuels. Water electrolysis for hydrogen production in an alkaline environment has attracted extensive attention because of its advantages of sufficient reactants, long-lasting products and high product purity. At present, PT-based catalysts have been considered to be the catalysts with the highest hydrogen evolution activity among many electrocatalysts. However, the reaction kinetics of HER in the alkaline environment are about 2-3 orders of magnitude lower than those in the acidic environment, and the internal mechanism of the HER process is unclear and divergent.
In this context, the construction of a two-site accelerated cleavage of H-OH molecules is a promising strategy to improve HER performance. The Ni-modified single crystal PT site has the potential to improve the performance of HER, and further exploration has shown that the improvement in performance can be attributed to the interfacial electronic synergy of the PT-Ni dual site for hydrogen bond formation. At the same time, the main ways to improve the activity of HER are to adjust the surface coordination environment of the co-site and rationally modify the electronic structure of the PT and Ni dual sites.
However, in the actual HER process, the alloy PT-M (M: transition metal) dual site is not enough to obtain excellent HO-H bond breaking performance. The disadvantage is that the M atom inserted into the PT lattice is easily assimilated by the adjacent PT atom and has little significant role as an additional participant in the HER process. Therefore, expanding the interatomic distance between the PT-M dual sites can exert its maximum effect through electron transfer and site synergy. Therefore, manufacturing remote dual sites is an effective way to take advantage of their synergistic effects.
Brief introduction of the results
We propose a strategy to construct remote PT-Ni dual sites by coating Ni(OH)2 on a high-index PT surface (HIFS), which not only increases the number of remote PT-Ni dual sites, but also changes the physicochemical properties of PT and Ni. The current density of the resulting PT-Ni two-site is 384 mA·cm-2, which is 7. higher than the specific activity of commercial PT C for HER in alkaline solution5 times. The improvement in HER performance is attributed to the synergistic catalysis of the PT-Ni two-site as well as unconventional electron coupling. Therefore, it is important to design an advanced catalyst by constructing Ni(OH)2-coated PT HIFS to fundamentally understand the synergistic effect of long-range PT-Ni dual sites.
**Reading guide
Fig.1 (a) Energy distribution of the hydrolysis process and (b) Geometry of the initial, transitional, and final states on the bare PT(111), PT(100), PT(100)-step bits, and PT-NI two-position matrices. (c) Plots are calculated based on Gibbs free energy for different site distances. Blue: pt, green: ni, white: o, red: h.
To test this hypothesis and provide theoretical guidance for this two-site catalyst, we used density functional theory (DFT) to model the rate-determining step (H-OH bond breakage) of the basic her. Firstly, the energy barriers (δg) of the hydrolysis process on three different PT surfaces: PT(111), PT(100), PT(100)-step site and PT-Ni double site were calculated, in order to elucidate the promoting effect of active site distance on basic HER. As can be seen from Fig. 1(a) and Fig. 1(b), the bond-breaking barriers δg of Ho-H at the PT(111), PT(100)-step, PT(100) and PT-Ni dual sites in water molecules are 0., respectively99 ev、0.91 ev、0.76 ev and 040 ev。
It can be clearly seen that the PT-Ni dual site has the lowest energy barrier for water dissociation, indicating that the Pt-Ni dual site is conducive to Ho-H bond cleavage. Compared with the pt(100) surface, the degree of hydrolysis δg on the pt(100) step surface was higher, indicating that the uncoordinated pt(100) site did not promote H-OH bond cleavage as well as the coordination-saturated pt(100) site. Figure 1(c) shows the site distances and the regularity with δg for different surface structures. The results show that within a certain range, the δg of hydrolysis has a linear relationship with the double-position distance. The PT-Ni two-site with the best performance has a site distance of approximately 35 , indicating that the long-distance PT-Ni dual site can be well matched by optimizing the adsorption configuration.
Fig. 2 TEM images of (A) PT nanoparticles, (B) HAADF-STEM, and (C) HRTEM. (D, F) TEM images of the PT-Ni dual site, and (E) HAADF-STEM images. (G-J) Nanoscale elemental mapping of PT-Ni dual sites. (K) TEM image of the PT-Ni two-locus. (l) False color processing of TEM images. (M) Pt-Ni two-site HRTEM image.
To test our theory**, we designed two types of catalysts: concave nanocube PT and Ni(OH)2-coated concave nanocube PT (remote PT-NI dual site). As shown in Figure 2(a), the transmission electron microscopy images show that the obtained PT nanoparticles are concave and cubic in shape and evenly dispersed, which is further revealed by high-angle annular darkfield scanning TEM images (Figure 2(b)).
At the same time, the average diameter size of PT nanocrystals is about 441nm, with more than 90% high morphology selectivity. Figure 2(c) shows a clear surface step in a single PT particle characterized by highly evolved TEM. The angles between the surfaces of the Pt nanocrystals are about 100 degrees, 120 degrees, 140 degrees and 160 degrees, which are consistent with the theoretical values of , , and surfaces.
In addition, long-distance PT-Ni dual-site was successfully prepared by wet chemical methods. As shown in Figure 2(D), membranous Ni(OH)2-coated PT nanoparticles can be clearly observed, as further evidenced by the HAADF-STEM image (Figure 2(e)), where the bright inner core is the PT nanocrystal, and the surrounding dark domain is the Ni(OH)2 film (Figure 2(F)).
It is worth noting that there is almost no change in the size of the particles. Elemental mapping at the nanoscale (Fig. 2(g)-2(j)) shows that Pt, O, and Ni are uniformly distributed across the Pt-Ni dual site. A significant contrast between the PT nucleus and the Ni(OH)2 membrane can be further observed from the individual particles in Figure 2(k) and Figure 2(L).
In addition, HRTEM also revealed the close interface structure between the PT nucleus and the Ni(OH)2 membrane. As shown in Figure 2(M), it can be clearly observed that the Ni(OH)2 membrane grows on the surface of the PT particles, forming abundant close contacts. The lattice spacing is 0196 nm and 0219 nm, corresponding to the (200) plane of PT and the (103) plane of Ni(OH)2·3H2O, respectively.
Figure 3: (A) XRD spectra and (B) XPS spectra of PT and PT-Ni dual sites. (c) Ratio of PT and PT-Ni two-site surfaces to Pt2+. (D) PDOS of surface PT atoms and D-band center positions of PT and PT-Ni duplex models. (e) Pt-Ni two-point charge density difference.
The PT-Ni two-site was characterized by X-ray diffraction (XRD). Figure 3(a) shows the XRD profile of the prepared PT and PT-Ni dual sites with a highly crystalline FCC PT phase. PT nanocrystals have the highest sum peak intensity. After Ni(OH)2 mixing, the crystal position of PT nanocrystals at the PT-Ni dual site was synchronized with that of pure PT, indicating that the modification of Ni(OH)2 did not change the crystal structure of PT nanocrystals. In addition, the 58° and 75° peaks of the PT-Ni dual site were observed to be typical crystal structures of Ni(Oh)2, demonstrating the presence of Ni(Oh)2.
Fig. 4 (A) HER curve, (B) specific activity and mass activity curves, (C) Tafel slope driven by commercial PT C, PT, and PT-Ni double-point polarization curves. (d) Normalized current-time (I-T) curves for PT and PT-Ni dual sites.
In 0The HER performance of the resulting PT-Ni two-site was tested in 1 M KOH solution. It is evident from Figures 4(a) and 4(b) that the intrinsic activity of the PT-Ni dual site and PT is 3., respectively84 and 246 mA·cm-2, which is 75 times and 48 times. As can be seen in Figure 4(b), the mass activity of the PT-Ni two-site is 052 mA·cm-2 is 52 times.
First, having a large number of uncoordinated surface PT atoms can provide abundant active sites for adsorbed water molecules, which indicates that the defective PT sites are beneficial for improving HER activity because the δG of hydrolysis is low. Secondly, the PT-Ni dual site has an abundant intimate interface between the defective PT site and the defective Ni(OH)2 nanometer sheet, and the dissociation of water can be accelerated by reducing the cleavage δg of water through the cocatalysis of the remote PT-Ni dual site.
As can be seen in Figure 4(D), the well-defined PT-Ni dual site remains at 84 after 8000 s of testingThe initial activity of 3% is higher than that of the PT catalyst of 636% activity. The enhanced HER durability further suggests that the Ni site is beneficial for stabilizing the surface structure of the PT site.
In the field of catalysis, excellent performance mainly depends on the degree to which the active site is matched to the reaction intermediate. Therefore, elucidating the long-range PT-Ni duplex structure-performance relationship is necessary to advance the basic research of nanoscience and nanocatalysis.
Therefore, after a detailed discussion of the above characterizations, the enhancement of HER performance should be attributed to the electronic effects and synergistic effects based on the remote PT-NI dual site. In terms of electronic effects, we noticed that after the introduction of Ni, the binding energy of PT is positively shifted compared with pure PT, which will optimize the adsorption behavior between the catalyst and the intermediate and promote the enhancement of performance. In addition to the electron effect, the synergistic effect also plays an important role in improving HER activity.
About the Author
Zhang PengfangHe graduated from Xiamen University in 2016 with a Ph.D. degree, mainly engaged in the research of cathode catalysts for metal-air batteries and zinc-iodine batteries. It has been published in ADV funct. mater.,nanoenergy，acs catal.，chem. eng. j.and other internationally renowned journals have published many articles**.
Wang Yao, Doctor of Engineering, Associate Professor, School of Chemical Engineering, Jiangnan University, Master's Supervisor. He is mainly engaged in the preparation of specific functional nano-single-atom materials and their applications in the field of energy electrocatalysis. He has published nearly 50 articles in top international journals such as Angew Chem Int ED, ADV Mater, Nano Lett, Acs Nano, Nano Energy, Acs Catal, Applied Catal B Environ, Nano Res and other top international journals, 4 of which have entered ESI Highly Cited, 5 of which have been cited more than 2,000 times, and the natural index is H=26. Participated in the writing of 2 academic monographs. He has presided over scientific research projects such as National Natural Science and Jiangsu Natural Science. He has been invited to serve as a guest editor of Rare Metals, a guest editor of Molecules, and a member of the Young Editorial Board of Exploration, Green Carbon, Rare Metals, Advanced Power Materials, and The Innovation.
Article information
liu c, zhang p, liu b, et al. long-range pt-ni dual sites boost hydrogen evolution through optimizing the adsorption configuration. nano research, 2023