Abstract
Protecting low coordinated sites (LCS) of Pt nanoparticles, which are vulnerable to dissolution, may be an ideal solution for enhancing the durability of polymer electrolyte fuel cells (PEMFCs). However, the selective protection of LCSs without deactivating the other sites presents a key challenge. Herein, we report the preferential protection of LCSs with a thiol derivative having a silane functional group, (3-mercaptopropyl) triethoxysilane (MPTES). MPTES preferentially adsorbs on the LCSs and is converted to a silica framework, providing robust masking of the LCSs. With the preferential protection, the initial oxygen reduction reaction (ORR) activity is marginally reduced by 8% in spite of the initial electrochemical surface area (ECSA) loss of 30%. The protected Pt/C catalyst shows an ECSA loss of 5.6% and an ORR half-wave potential loss of 5 mV after 30,000 voltage cycles between 0.6 and 1.0 V, corresponding to a 6.7- and 2.6-fold durability improvement compared to unprotected Pt/C, respectively. The preferential protection of the vulnerable LCSs provides a practical solution for PEMFC stability due to its simplicity and high efficacy.
Highlights
Accepted: 24 February 2021Polymer electrolyte membrane fuel cells (PEMFCs) have been used in automobile and stationary applications due to their advantages of high efficiency, zero emissions, and moderate operation conditions [1,2]
We demonstrate the feasibility of preferential protection by density functional theory (DFT) calculations and experimentally demonstrate that the suggested simple post-treatment, which is applicable to various types of Pt catalyst, significantly enhances the durability of Pt/C with marginal activity loss
(100) planes, the (211) plane exposes the ledges of the stepped surfaces, which act as preferential adsorption sites for MPTES due to the lower coordination numbers of their Pt atoms
Summary
Accepted: 24 February 2021Polymer electrolyte membrane fuel cells (PEMFCs) have been used in automobile and stationary applications due to their advantages of high efficiency, zero emissions, and moderate operation conditions [1,2]. In current PEMFCs, platinum nanoparticles (NPs) supported on carbon materials (Pt/C) are commonly used as an oxygen reduction reaction (ORR) catalyst for the cathode due to their high catalytic activity. Under normal PEMFC operation conditions, Pt NPs are gradually degraded, resulting in a loss in electrochemical surface area (ECSA) and ORR activity. Pt dissolution occurs due to the intrinsic electrochemical and chemical instability of Pt. NP surfaces under potential drift, and the highly acidic conditions of the PEMFC (Figure 1a). According to the phase–pH diagram of Pt NPs, Pt oxide (PtOx ) is spontaneously formed at higher potentials, triggering Pt dissolution [7,8,9]. In the oxide formation process, placeexchange of Pt and oxygen leads to exposure of the Pt atom of PtOx to the surface, which is prone to Pt dissolution due to its high surface energy. The oxides are Published: 4 March 2021
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