Tailoring a Three-Phase Microenvironment for High-Performance Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells

Abstract

Proton exchange membrane fuel cells (PEMFCs) offer an attractive zero-emission mobile power source. However, the requirement of excessive platinum group metal (PGM) catalysts to facilitate the sluggish oxygen reduction reaction (ORR) in PEMFCs has prevented their widespread adoption. Despite tremendous progress in catalyst development with greatly increased catalytic activities, the reduction of PGM loading in practical PEMFCs remains a challenge. The ORR in PEMFCs occurs at a catalyst-electrolyte-gas three-phase interface, with multi-faceted challenges involving the activity of the catalysts, available active sites, and concerted transport of the reactants (oxygen, protons) to and removal of the product (water) from the active sites. The reduction of PGM loading reduces the number of catalytic sites, requiring a higher reaction rate on each site to sustain the overall power output, which in turn necessitates faster delivery of the reactants to and removal of the products from each active site. A desirable interface must allow efficiently feeding oxygen and protons to the catalytic sites without starving the reaction and must allow timely removal of water to avoid interface flooding. Herein we report the design of the three-phase microenvironment in PEFMCs by tailoring the interactions between the carbon supports and the electrolyte ionomers. We show that the carbon surface with 2.4% oxygen interacts with the ionomers through both its hydrophilic and hydrophobic regions, creating favorable transport paths for rapid delivery of both oxygen and protons, and timely removal of water. Such an elaborated interfacial design allows reducing costly platinum catalysts while maintaining state-of-the-art performance. For the first time we demonstrate PEMFCs with all key ORR catalyst performance metrics, including mass activity, rated power and durability, surpassing the U.S. DOE targets.

A Molecular Model of PEMFC Catalyst Layer: Simulation on Reactant Transport and Thermal Conduction

“…In this paper, the water cluster morphology is given via the water molecular density contours after the dynamics simulation. Moreover, the connecting threshold is set to 2 Å, referring to the 3.5 Å in literature [ 27 ] and 1.4 Å in [ 37 ]. The water cluster morphology diagrams are demonstrated in Figure 8 and the yellow isosurface represents the water clusters region.…”

“…As for numerical simulation research, analytical models [ 13 , 14 ], mesoscopic methods such as lattice Boltzmann method (LBM) [ 15 , 16 ], microscopic methods such as molecular dynamics (MD) [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ] simulation, and density functional theory (DFT) [ 28 , 29 , 30 , 31 ] are usually used to construct the CL structure and study the mechanisms of reactant transport, reaction, and heat conduction. For example, Liang et al [ 14 ] proposed the fractal theory of porous media to quantify the effective electrolyte diffusivity in porous media with consideration of the electrical double layer (EDL) effects.…”

“…He also studied the effects of side chain length on the thermal conductivity of the perfluorosulfonic acid (PFSA) membrane in another paper [ 26 ]. Zhao et al [ 27 ] used the oxidized graphite to design a three-phase microenvironment in CL by MD simulation and experiments. Taeyoon et al [ 29 ] calculated the adsorption characteristics and electron transfer of the catalysts with optimized geometry using the density functional theory (DFT) with carbon nanotube added in the CL.…”

Chemical Identification of Catalytically Active Sites on Oxygen‐doped Carbon Nanosheet to Decipher the High Activity for Electro‐synthesis Hydrogen Peroxide

“…[4,5] Furthermore,t his anthraquinone technique operating in centralized plants leads to the additional cost to transport H 2 O 2 .R ecently,d irect electrosynthesis H 2 O 2 through two-electron (2 e À )oxygen reduction reaction (ORR) driven by renewable electricity has been regarded as an emerging alternative to traditional anthraquinone process due to the environmentally friendly operation and on-site productivity. [6][7][8][9][10][11] In recent years,e normous efforts have been devoted to searching for cost-effective and high-performance electrocatalysts to produce H 2 O 2 . [12][13][14][15][16][17] Noble-based catalysts,such as Pd-based [18][19][20] and Pt-based [21,22] materials,s how high ORR activity and H 2 O 2 selectivity in wide range of pH, but their low abundance and high cost impede the large-scale commercial applications.R ecently,c arbon materials have been identified as the promising electrocatalysts for H 2 O 2 electrosynthesis owing to their low cost, high reusability and adjustable nanostructure/interface.…”

Engineering Carbon Materials for Electrochemical Oxygen Reduction Reactions

“…In this way, O 2 is reduced by the electrons (Figure 1a). [4] The efficiency of these energy devices is usually determined by that of the ORR process. However, the strong bond energy of OO (498 kJ mol −1 ) means that the ORR at the electrode is not easy, especially compared to the hydrogen oxidation reaction (HOR: H 2 →2H + + 2e − ) at the anode of hydrogen-oxygen fuel cells (Figure 1a).…”