Revealing the concentration of hydrogen peroxide in fuel cell catalyst layers by an in-operando approach

doi:10.1016/S1872-2067(21)63993-1

Abstract

Abstract:

To evaluate the H₂O₂-tolerance of non-Pt oxygen reduction reaction (ORR) catalysts as well as investigate the H₂O₂-induced decay mechanism, the selection of an appropriate H₂O₂ concentration is a prerequisite. However, the concentration criterion is still unclear because of the lack of in-operando methods to determine the actual concentration of H₂O₂ in fuel cell catalyst layers. In this work, an electrochemical probe method was successfully established to in-operando monitor the H₂O₂ in non-Pt catalyst layers for the first time. The local concentration of H₂O₂ was revealed to reach 17 mmol/L, which is one order of magnitude higher than that under aqueous electrodes test conditions. Powered by the new knowledge, a concentration criterion of at least 17 mmol/L is suggested. This work fills in the large gap between aqueous electrode tests and the real fuel cell working conditions, and highlights the importance of in-operando monitoring methods.

Key words: Fuel cells, Oxygen reduction reaction, Non-Pt catalyst layer, H₂O₂ concentration, In-operando monitoring, Catalyst degradation

Chun-Yu Qiu, Li-yang Wan, Yu-Cheng Wang, Muhammad Rauf, Yu-Hao Hong, Jia-yin Yuan, Zhi-You Zhou, Shi-Gang Sun. Revealing the concentration of hydrogen peroxide in fuel cell catalyst layers by an in-operando approach[J]. Chinese Journal of Catalysis, 2022, 43(7): 1918-1926.

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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(21)63993-1

https://www.cjcatal.com/EN/Y2022/V43/I7/1918

Figures/Tables 5

Fig. 1. Schematic of the electrochemical probe method to in-operando monitor the H2O2 concentration in the fuel cell catalyst layer. The single-cell consists of bipolar plate (BPP), GDL, microporous layer (MPL), anode and cathode catalyst layers (CL), and proton exchange membrane (PEM). The probe electrode consists of a Pt wire (0.1 mm in diameter) with the end connecting with a Pt net (0.16 cm2 in geometric area). The Pt wire was sealed in a PTFE tube. The Pt net was electronically insulated with a cellulose membrane and sandwiched between the PEM and the catalyst layer. Once the ORR occurred in the cathode catalyst layer, the 2e- ORR product (H2O2) will pass through the cellulose membrane to reach the Pt net electrode to be oxidized then.

Fig. 2. (a) The plot of the cell voltage and the current versus the operation time (t) for a H2-O2 PEMFC with Pt/C as the cathode catalyst (bottom); the H2O2 oxidation current from the probe electrode versus t (top). (b) Five repeated polarization curves of the PEMFC test (bottom) and the H2O2 oxidation current detected by the probe electrode (top). Test conditions: 60 °C (cell temperature); 0.5 bar backpressure; 0.2 standard liter per minute (SLPM) with 150% RH for both H2 and O2; two layers of N211 membrane; 0.4 mg cm-2 of Pt for both cathode and anode; 1.2 VRHE (probe electrode potential), 1.21 cm2 (MEA active area), 0.16 cm2 (Pt net geometric area). (c) External standard curve of the H2O2 oxidation current versus the H2O2 concentration obtained in a single cell at 60 °C. (d) H2O2 concentration in the Pt/C cathode catalyst layer at different cell voltages. The first cycle was selected to calculate the concentration of H2O2.

Fig. 3. (a) Bottom: the polarization curves of a H2-O2 PEMFC test with the Fe/N/C as the cathode catalyst; Top: H2O2 oxidation current from the probe electrode at different cell voltages. (b) H2O2 concentration in the Fe/N/C catalyst layer at different cell voltages. The first cycle was selected to calculate the concentration of H2O2. Test conditions. 60 °C (cell temperature); 0.5 bar back pressure; 0.2 SLPM with 150% RH for both H2 and O2; two layers of N211 membrane; Fe/N/C catalyst (cathode, 4.0 mg cm-2), Pt/C catalyst (anode, 0.4 mgPt cm-2), 1.2 VRHE (probe electrode potential). 1.21 cm2 (MEA active area), 0.16 cm2 (Pt net geometric area).

Fig. 4. (a) Life test at a cell voltage of 0.4 V for a H2-O2 PEMFC with the Fe/N/C as the cathode catalyst. (b,c) Oxidation current signals of H2O2 on the probe electrode at different time intervals during the life test. The first 0.3 h is shown in Fig. 4(b). The following 4.2 h is shown in Fig. 4(c). (d) The variation of the local H2O2 concentration in the Fe/N/C catalyst layer during the fuel cell life test. The H2O2 concentration at t = 0 h was extracted from the polarization experiment in Fig. 3.

Fig. 5. Comparison of H2O2 concentration between RRDE test and fuel cell working conditions. Fuel cell working voltage: 0.4 V (The operation conditions are the same as Fig. 4). Fe/N/C catalyst loading: 0.06 mg cm-2 (RRDE) vs. 4.0 mg cm-2 (fuel cell working conditions).

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