1. School of Chemistry and Chemical Engineering, in-situ Center for Physical Sciences, Frontiers Science Center for Transformative Molecules, Shanghai Jiao Tong University, Shanghai 200240, China;2. College of Chemistry and Molecular Sciences, Hubei Key Lab of Electrochemical Power Sources, Wuhan University, Wuhan 430072, China;3. The Institute for Advanced Studies, Wuhan University, Wuhan 430072, China;4. Sauvage Center for Molecular Sciences, Wuhan University, Wuhan 430072, China
Abstract:
Fuel cells are essential energy conversion devices for future renewable energy structures. Mainstream proton exchange membrane fuel cells (PEMFCs) generally exhibit satisfactory performance despite requiring noble metal catalysts to be stable in acidic environments. Alkaline polymer electrolyte fuel cells (APEFCs), in contrast, offer the benefit of employing non-noble metal catalysts in fuel cells, but their overall performance and especially their long-term stability require further improvement. A critical component within APEFCs is the membrane electrode assembly (MEA), which comprises a hydroxide ion conductive polymer membrane, a cathode, and an anode (including a catalyst layer and a gas diffusion layer). MEA is where electrochemical reactions occur; thus, it plays a crucial role in determining fuel cell performance. Herein, the fabrication of a cone-shaped array on the surface of an alkaline polymer electrolyte membrane for improving the overall device performance is presented. The cone array was prepared using a sacrificial anodic aluminum oxide (AAO) template, and the array side of the polymer electrolyte was used as the cathode to construct the MEA, denoted as A-MEA. The control sample with no cone arrays on the polymer electrolyte surface is denoted as P-MEA. The Pt loadings on both the anode and cathode sides were approximately 0.2 mg∙cm−2. APEFCs with A-MEA and P-MEA were separately assembled and tested in an 850e Fuel Cell Test System at a cell temperature of 80 ℃. Fully humidified hydrogen and oxygen were both supplied at a flow rate of 1000 mL·min−1. The back pressure for both the anode and the cathode was 0.2 MPa. As a result, the APEFC with A-MEA exhibited a higher peak power density than that of the APEFC with P-MEA (1.48 vs. 1.04 W∙cm−2). The enhanced electrochemical performance of the APEFC with A-MEA was ascribed to the array-structured cathode, which improved the hydrophilicity of the polymer electrolyte membrane and increased the utilization efficiency of the catalyst. The hydrophilicity of the polymer electrolyte membrane with cone arrays was confirmed using contact angle measurements. The contact angles of the membranes with and without cone arrays were ~0° and 70.8°, respectively. The hydrophilic membrane promotes the electrode reaction at the cathode side. The electrochemically active surface area (ECSA) was also measured using cyclic voltammetry (CV) between 0.08 and 1 V (vs. reversible hydrogen electrode, RHE) at a scan rate of 20 mV∙s-1, using fully humidified H2 and N2. A flow rate of 1000 mL∙min−1 and back pressure of 0 MPa were employed. Results revealed that the ECSA of the cathode without the array was smaller than that of the array-structured cathode (21.17 vs. 24.89 m2∙g−1), indicating that the array structure improved the catalyst utilization efficiency compared to that of the control sample. This study provides an effective strategy for the structural design and optimization of the MEAs in APEFCs.
