Mechanism of Water Content on the Electrochemical Surface Area of the Catalyst Layer in the Proton Exchange Membrane Fuel Cell

Abstract

Combined molecular dynamics (MD) simulation and experiment are adopted to gain the mechanism of water content on the electrochemical surface area (ECSA) of the catalyst layer in a proton exchange membrane fuel cell. The morphology of water domains in the catalyst layer has a strong impact on the ECSA via MD simulation. The morphology of the water domains is isolated water clusters at low water content, resulting in the poor ECSA due to the lack of proton transport paths. The transport paths of protons tend to be quickly established with increasing water content during the transition process of the morphology of water domains from isolated water clusters to the water channel network, thereby leading to the rapid increase of the ECSA. However, the slight increase of the ECSA at high water content mainly results from the improved contact area between water domains and Pt particle instead of the formation of new transport paths. In addition, the stronger binding of water molecules and the Pt particle at low temperature results in a higher ECSA.

Effect of Stratification of Cathode Catalyst Layers on Durability of Proton Exchange Membrane Fuel Cells

“…MEA #5 showed the highest ECSA (81.81 m 2 /g Pt ) of the stratified MEAs at 100% RH. The increase in ECSA with RH was also reported by Fan et al [22], who mainly attributed this trend to the improved contact area between Pt particles and water domains instead of the formation of new transport pathways. The low porosity and denser agglomerate structure of MEA #5 could have played a role in increasing the contact area between water domains and ionomer/catalyst aggregates.…”

Pt utilization in proton exchange membrane fuel cells: structure impacting factors and mechanistic insights

“…42,43 In the meantime, computational approaches such as molecular dynamics simulation also provide helpful insights into the ionomer nanostructures of the ionomer in CL. [44][45][46] The conclusions reached are that the ionomer is inclined to form a thin adhesive film with a thickness of several nanometer mainly on the Pt surface with negligible internal porosity.…”

Towards the digitalisation of porous energy materials: evolution of digital approaches for microstructural design

“…151 The material properties predicted by MD models greatly contribute to the in-service model of energy devices by indicating relationships between different physical variables, for example, the quantitative relationship between relative humidity and electrochemical surface area in fuel cells. 150 As classic MD is designed for simulations at the time scale around tens of ns, for slower processes outside this timescale range, kinetic Monte Carlo (KMC) models have often been employed as well. 156 3.3.2 Mesoscopic models.…”

“…This method relies on the solution of the Newton's equations of motion for all atoms in order to extract path-dependent processes of materials. Fan et al 150,151 employed MD to predict the electrochemical surface area of porous CLs in PEMFCs under different humidity conditions, and the oxygen transport/thermal conductivity for a perfluorosulfonic acid membrane, as shown in Fig. 7b.…”

“…7 Results of various physical models that were used to predict properties of porous energy materials. (a) Eu clustering-layer-incorporated and formation energies in perovskite solar cells (DFT) 143 (reproduced with permission from the American Association for the Advancement of Science); (b) structures of CL and electrochemical surface area (MD) 150 (reproduced with permission from ACS Publications); (c) effective diffusivity of perforated GDLs (LBM) 158 (reproduced with permission from Elsevier); (d) structure of blend membrane and proton conductivity (DPD) 163 (reproduced with permission from Royal Society of Chemistry); (e) effective diffusivity of wet GDLs 164 (reproduced with permission from IOP Publishing); (f) structural evolution of an SOFC electrode and three-phase boundary fraction (PFM) 166 (reproduced with permission from AIP publishing); (g) structural evolution of electrode of Li-ion battery in calendaring process 167 (reproduced with permission from Elsevier).…”