Engineering the membrane electrode assembly of direct methanol fuel cells using novel graphene architecture

• Main Author: Balakrishnan, Prabhuraj
• Other Authors: Holmes, Stuart ; Siperstein, Flor
• Published: University of Manchester 2018
• Subjects: 660
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.764654

This research focuses on improving direct methanol fuel cell (DMFC) performance by using graphene based materials in their membrane electrode assembly (MEA). The main obstacles of commercialization, poor electrode kinetics and the fuel crossover are addressed by using reduced graphene oxide (rGO) in the cathode microporous layer and single layer graphene (SLG) as an anode barrier layer. In the microporous layer work, an rGO (by hydroiodic acid (HI) reduction of graphene oxide) coated electrode exhibited higher conductivity than conventionally used Ketjen Black electrode (standard). The MEA containing rGO produced peak power density of 79 ± 3 mW cm-2 compared to the standard MEA performance of 55 ± 3 mW cm-2 (44 % improvement) at 70 °C, 1 M methanol fuel cell operating conditions. Doping rGO with boron (B-rGO) or nitrogen (N-rGO) by boric acid and nitric acid treatment and utilizing them as electrodes produced peak power density of 90 ± 3 mW cm-2 for B-rGO (63 % improvement) and 101 ± 3 mW cm-2 for N-rGO (84 % improvement) respectively. This is attributed to the higher conductivity of doped rGO electrodes than rGO, owing to the replacement of heteroatoms in their graphene lattice, with detected boron and nitrogen levels at 2 at% and 6 at%, evidenced by x-ray photoelectron spectroscopy (XPS), aiding in improved electron transfer. In the barrier layer work, SLG added onto the anode side of the MEA, reduced methanol permeation from 1.72 ± 0.1 x 10-7 mol cm-2 s-1 (for the standard) to 1.21 ± 0.1 x 10-7 mol cm-2 s-1, with negligible resistance to protons observed at 70 °C, leading to 45 % improvement in power density (77 ± 1 mW cm-2), caused by the dense carbon lattice packing and single layer nature of SLG. Preliminary results using hexagonal boron nitride (hBN), showed that the cell performance improved by 18 %. Overall, it is evident from the performance improvement results that these graphene materials (first ever reported to have used in the MEA of a DMFC) hold great promise for paving the way towards DMFC commercialization by increasing the electrode kinetics (in case of rGO usage) and reducing methanol permeation (in case of SLG usage).