Pt-Based Intermetallic Nanocrystals in Cathode Catalysts for Proton Exchange Membrane Fuel Cells: From Precise Synthesis to Oxygen Reduction Reaction Strategy

Abstract

Although oxygen reduction reaction (ORR) catalysts have been extensively investigated and developed, there is a lack of clarity on catalysts that can balance high performance and low cost. Pt-based intermetallic nanocrystals are of special interest in the commercialization of proton exchange membrane fuel cells (PEMFCs) due to their excellent ORR activity and stability. This review summarizes the wide range of applications of Pt-based intermetallic nanocrystals in cathode catalysts for PEMFCs and their unique advantages in the field of ORR. Firstly, we introduce the fundamental understanding of Pt-based intermetallic nanocrystals, and highlight the difficulties and countermeasures in their synthesis. Then, the progress of theoretical and experimental studies related to the ORR activity and stability of Pt-based intermetallic nanocrystals in recent years are reviewed, especially the integrated strategies for enhancing the stability of ORR. Finally, the challenges faced by Pt-based intermetallic nanocrystals are summarized and future research directions are proposed. In addition, numerous design ideas of Pt-based intermetallic nanocrystals as ORR catalysts are summarized, aiming to promote further development of commercialization of PEMFC catalysts while fully understanding Pt-based intermetallic nanocrystals.

Pt-Based Oxygen Reduction Reaction Catalysts in Proton Exchange Membrane Fuel Cells: Controllable Preparation and Structural Design of Catalytic Layer

“…In most studies, Pt-based alloys are usually disordered structures with Pt and transition metals randomly distributed in NPs. However, acidic environments (pH < 1) and high chemical potentials (>0.7 V RHE ) can lead to the dissolution and oxidation of transition metals, thus reducing the overall activity of the catalyst [ 110 , 111 ]. Therefore, the ordered Pt-based alloy catalysts, such as Pt 3 Co [ 74 , 112 ], Pt 3 Fe [ 113 , 114 ], Pt 3 Cu [ 115 , 116 ], etc., have attracted more and more attention.…”

Microwave Heating of Nanocrystals for Rapid, Low-Aggregation Intermetallic Phase Transformations

“…Intermetallic nanocrystals (NCs) are one of the most studied classes of materials for electrocatalysis − due to their high electrochemical stability − at lower precious metal loadings. ,,,− Pt–Co intermetallic face-centered-tetragonal (fct) phase (L1 0 ) NCs have been demonstrated as viable electrocatalysts for the oxygen reduction reaction (ORR). ,− The ability to perform the ORR with high electrochemical stability while decreasing the Pt loading is of key importance for proton exchange membrane fuel cells (PEMFCs), ,,− with the capability of providing a source of clean energy able to compete with fossil fuels . To make PEMFCs economically viable, there is a need to optimize the activity of the catalyst per unit Pt, , also known as the mass activity.…”

“…We use near-monodisperse Cu-doped PtCo 2 NCs in the intermetallic L1 0 phase as a model system. Copper-doping is known to reduce the barrier associated with the phase transformation. ,, The L1 0 phase is desirable because of simultaneously higher electrochemical stability and lower cobalt leaching during catalysis than the random alloy (A1) phase. − ,− ,,,, Typically, as-synthesized A1 face-centered-cubic (fcc) phase NCs are transformed into intermetallic L1 0 NCs by a thermal treatment that involves temperatures exceeding 400 °C over several hours. ,,,,, During this process, NC aggregation, or sintering, occurs, leading to a decrease in the electrochemically active surface area (ECSA) and resulting in a decrease in mass activity for the ORR. ,,, Several literature reports have attempted to prevent NCs from aggregating during the thermal treatment by anchoring the NCs to the substrate, ,, or by synthesizing the NCs directly in the intermetallic phase. ,,− Other methods have demonstrated a monodisperse dispersion of intermetallic NCs; however, these require a specialized technique such as Joule heating or electrochemical dealloying. ,− So far, no method has shown a complete phase transformation with minimized aggregation.…”

“…7,13−18 The ability to perform the ORR with high electrochemical stability while decreasing the Pt loading is of key importance for proton exchange membrane fuel cells (PEMFCs), 10,14,19−21 with the capability of providing a source of clean energy able to compete with fossil fuels. 22 To make PEMFCs economically viable, there is a need to optimize the activity of the catalyst per unit Pt, 14,22 also known as the mass activity.…”

“…1,2,6,13,26,27 During this process, NC aggregation, or sintering, occurs, leading to a decrease in the electrochemically active surface area (ECSA) and resulting in a decrease in mass activity for the ORR. 2,7,13,14 Several literature reports have attempted to prevent NCs from aggregating during the thermal treatment by anchoring the NCs to the substrate, 11,20,21 or by synthesizing the NCs directly in the intermetallic phase. 14,15,28−32 Other methods have demonstrated a monodisperse dispersion of intermetallic NCs; however, these require a specialized technique such as Joule heating 33 or electrochemical dealloying.…”