2020-01-17 high stability Reduction Catalyst PTC catalyst
2020-01-17 high stability Reduction Catalyst PTC catalyst
Platinum based nanomaterials are still the most feasible catalysts for oxygen reduction reactions (ORR) and the most critical materials for proton exchange membrane fuel cells (PEMFCs). However, for platinum based catalysts, due to its limited reserves, high price, poor stability and easy to be poisoned and many other factors, the development of fuel cells is seriously restricted. Therefore, how to improve the activity and durability of catalysts, reduce the amount of precious metals, and effectively reduce the cost of fuel cell manufacturing has become a research hotspot in recent years.
At present, the commonly used strategies to improve the electrocatalytic activity and durability of Pt based catalysts mainly include: (1) component control; (2) crystal surface control; (3) morphology control. It is worth noting that most of the current reports on Pt based electrocatalysts with high activity and durability focus on the doping of transition metals and the formation of Pt alloys. At present, there are few reports about Pt based catalysts doped with non-metallic elements, especially on n-doped Pt based materials.
Recently, Ningbo Zhongke innovative energy technology Co., Ltd. and Yang Hui research team of Shanghai Institute of higher learning, Chinese Academy of sciences have developed a n-doped Pt / C catalyst with high oxygen reduction stability. The catalyst prepared by the liquid phase method shows the activity comparable to the commercial Pt catalyst and excellent stability. After 20000 accelerated cycle durability tests (ADT), the mass specific activity decay is only 3.7%, which is far lower than that of commercial platinum carbon catalyst. It is particularly noteworthy that this method is simple and does not use surfactants. In this paper, the catalyst has been prepared in a single batch of 100g level. Recently, the company has been able to achieve kg level preparation, and the load of Pt can be 10 ~ 100wt%. Therefore, this promising preparation strategy provides great potential for the production of Pt based catalysts economically and efficiently, and opens a window for large-scale application. Relevant papers were published in Journal of catalysis.
Fig. 1. Schematic illustration of the synthetic strategy of N-doped Pt/C catalysts. XPS and EXAFS showed that pt-n bond existed in Pt / C catalyst. In addition, the XRD results show that the (11) crystal surface of Pt in the catalyst has a negative shift of 0.23o compared with the commercial platinum carbon catalyst. The crystal lattice of Pt in the synthesized Pt / C catalyst was obviously distorted, and the N signal was detected in the Pt particles by EELS spectrum. It is found by calculation that the crystal surface spacing of Pt (11 1) is 0.232 nm, which is about 1.3% higher than that of commercial Pt / C at 0.229 nm. It is believed that N atom is doped into the lattice of Pt atom, and N doping increases the crystal surface spacing of Pt lattice, resulting in lattice tensile strain effect.
Fig. 2. (a) XPS spectra for N 1s in N-doped Pt NPs/C. (b) XPS spectra for Pt 4f in N-doped Pt NPs/C and N-doped Pt NPs/C-H2. (c) XRD diffraction patterns of different catalysts. (d) Enlarged region of the (111) diffraction peaks of Fig. 2c. (e) Pt L3-edge XANES for all the samples. (f) The k3-weighted R-space Fourier-transform EXAFS spectra of different catalysts and reference samples.
Fig. 3. (a) High resolution HAADF-STEM image of N-doped Pt NPs. (b) HAADF-STEM image of one N-doped Pt NP. (c) N element K-edge EELS spectrum of the N-doped Pt NP in Fig. 3b. (d) The integrated pixel intensity taken along the Pt (111) spacing direction marked by purple square in Fig. 3b. Inset of Fig. 3d is FFT pattern from the purple square at the Pt NP shown in Fig. 3b.
Then, the orr electrocatalytic activity and stability of the n-doped Pt / C catalyst were compared with that of the commercial Pt-C catalyst. The n-doped Pt nanoparticles exhibit orr activity comparable to commercial platinum carbon catalysts and excellent durability. Its ECSA is similar to that of commercial platinum carbon catalyst (FIG. 4A); the orr mass specific activity at 0.9V (vs. rhe) potential is 5% higher than that of commercial Pt / C (Fig. 4b). After 20000 accelerated durability cycle tests, it was found that the ECSA of the n-doped Pt nanoparticles decreased only 11.5%, which was significantly lower than that of the commercial JM platinum carbon catalyst (Fig. 4e); and the orr mass specific activity at 0.9v/rhe decreased only 3.7%, which was significantly lower than that of the commercial JM platinum carbon catalyst (30.9%) (Fig. 4F), making it one of the most stable Pt / C electrocatalysts reported. In the hydrogen air fuel cell single cell test, when the current density of the cell is 1.4 a · cm-2, the voltage is 0.65 V (as shown in Fig. 4G).
DFT theoretical calculation shows that the doping of N atoms induces the lattice tensile strain effect, which leads to the transfer of electrons on Pt to N, and the weakened interaction between Pt atoms due to the electron repulsion. Compared with pure Pt, the binding energy and desorption energy between Pt atoms in n-doped Pt nanoparticles are higher, so the surface Pt atoms are more difficult to be dissolved and the catalyst stability is better in the orr process (Figure 5).
It is worth noting that most of the reported Pt based catalysts are still based on the gram or even milligram level. However, the preparation method introduced in this paper is simple and does not use surfactant. It has been realized in the actual production of Ningbo zhongkechuangxin Energy Technology Co., Ltd. in a single batch of 100g level preparation (as shown in Figure 6).
Fig. 4. (a) CVs of different catalysts in 0.1 M HClO4 solution at a scan rate of 50 mV∙s-1. (b) ORR polarization curves on different catalysts in O2-saturated 0.1M HClO4 with a scan rate of 10 mV∙s-1 and rotation speed of 1,600 rpm. (c-d) ORR polarization curves on different catalysts before and after 20,000 ADT cycles between 0.6 and 1.1 V/ RHE. (e) The changes in ECSAs of the different catalysts before and after 20,000 cycles. (f) The changes in mass activities of the different catalysts before and after 20,000 cycles. (g) Single cell performance of H2-air fuel cells prepared with N-doped Pt/C and commercial JM Pt/C. (Pt loading: anode-0.1 mg·cm-2; cathode-0.3 mg·cm-2. Testing condition: 80 oC, 100 RH%, back-pressure=1 atm.)
Fig. 5. (a) Pure Pt NP and (b) N-doped Pt NP. The grey and red balls stand for the Pt and N atoms, respectively. (c) The tensile strain of Pt NP as a function of the number of N atoms embedded into the NP. (d) Atom removal energy of pure Pt NP and N-doped Pt NP at different atom positions (a, b, c and d represent the Pt atom position sites shown in Fig. S25). (e) Reaction free energy diagram of the ORR for two different reactive sites on N-doped Pt NPs.
Fig. 5. The scene photograph of synthesizing the N-doped Pt NPs in a large-scale.
original text： N-doping induced tensile-strained Pt nanoparticles ensuring an excellent durability of the oxygen reduction reaction Yunjie Xiong, Yunan Ma, Liangliang Zou, Shaobo Han, Hong Chen, Shuai Wang, Meng Gu, Yang Shen, Lipeng Zhang, Zhenhai Xia, Jun Li and Hui Yang Journal of Catalysis, 2020, 382: 247-255 DOI: 10.1016/j.jcat.2019.12.025
Ningbo zhongkeke innovative energy technology Co., Ltd. focuses on the development and production of high-performance noble metal based nano catalysts with independent intellectual property rights. The company focuses on the application demand of high activity and long durability nano structure catalysts in the fields of proton exchange membrane fuel cell, solid electrolyte water electrolysis, pharmaceutical hydrogenation, chemical industry, etc., and develops a variety of practical noble metal based nano catalysts Catalysts (PT, PD, Au, IR, Ru, etc.). The company has a number of core patent technologies for catalyst preparation with independent intellectual property rights, and launched high metal load catalyst products, which are applicable to hydrogen oxygen proton exchange membrane fuel cells, direct methanol fuel cells, metal air fuel cells and solid electrolyte water electrolysis for hydrogen production. The main technical indicators have reached or exceeded the international advanced level. The company's main products won the silver medal of the 19th industrial exposition.