Abstract
The advent of the Hydrogen Society created great interest around hydrogen-based energy a decade ago, with several types of vehicles based on hydrogen fuel cells already being produced in the automotive sector. For highly efficient fuel cell systems, the control of hydrogen inside a polymer-based electrolyte membrane is crucial. In this study, we investigated the molecular behavior of hydrogen inside a polymer-based proton-exchange membrane, using quantum and molecular dynamics simulations. In particular, this study focused on the structural difference of the pendent-like side chain polymer, resulting in the penetration ratio of hydrogen into the membrane deriving from the penetration depth of the membrane’s thickness while keeping the simulation time constant. The results reveal that the penetration ratio of the polymer with a shorter side chain was higher than that with the longer side chain. This was justified via two perspectives; electrostatic and van der Waals molecular interactions, and the structural difference of the polymers resulting in the free volume and different behavior of the side chain. In conclusion, we found that a longer side chain is more trembling and acts as an obstruction, dominating the penetration of hydrogen inside the polymer membrane.
Highlights
Hydrogen, as an energy resource, can make life significantly more eco-friendly
The results reveal that membranes based on polymer containing shorter side chains led to a higher penetration ratio than that of longer side chains
In this study, we focused on the structural effect of the side chain on hydrogen permeation, aiming to improve the design of polymer electrolyte membranes
Summary
The hydrogen fuel cell was introduced by William Robert Grove 180 years ago [1], numerous potential applications have recently raised extreme engagement from many researchers, in various industrial sectors [2]. Automotive systems based on hydrogen fuel cells can already be found on the road, with examples such as “NEXO” produced by Hyundai Motor Company or “MIRAI” by Toyota representing the upcoming hydrogenbased automotive future. A hydrogen fuel cell works based on electrochemistry, by passing hydrogen through the anode and oxygen through the cathode of the cell. Electrical power is generated via three simple steps: (i) the dissociation of hydrogen to the proton and electron; (ii) the conduction of electrons through electronic channels and protons through a proton-exchange membrane; and (iii) the synthesis of water by a proton, electron, and oxygen. A polymer electrolyte membrane for fuel cell (PEMFC) is commonly used in vehicles due to better operation at relatively low temperature, while other types of fuel cells (such as alkaline cell, phosphoric acid fuel cell, molten carbonate cell, direct methanol fuel cell and solid oxide cell) require a higher operation temperature [3,4]
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