Modeling of high-efficient direct methanol fuel cells with order-structured catalyst layer

Abstract

Direct methanol fuel cell is widely seen as the promising energy conversion technology with high energy efficiency, low emission and easy delivery of fuel. However, catalysts in traditional direct methanol fuel cell associating with disordered electrode are prone to agglomerate, lowering energy conversion efficiency. Herein, we focus on order-structured catalyst layer by presenting a two-dimensional, two-phase, steady-state model to shed light on the ordered direct methanol fuel cells. The model considers both radial and axial transports of oxygen along the carbon nanowire in the order-structured cathode catalyst layer. The radial diffusion model simulates the oxygen transfer from the gas pore to the triple-phase boundary of the cylindrical electrode covered by a water film. The model also accounts for the effects of electrochemical surface areas of catalysts and the volume fraction of three phases. The whole-cell model formed by integrating those in different regions is solved numerically and validated against the experimental data in the literature. It is demonstrated that the direct methanol fuel cell with ordered electrode yields a better cell performance, 46.6% and 62.5% higher than that with agglomerate electrode in terms of peak power density and maximum current density, respectively, implying the improved energy efficiency. The better performance of the ordered electrode is attributed to the lowered activation, ohmic and concentration losses. Overall effect of the structural parameters indicates that the peak power density of the ordered direct methanol fuel cell can reach 93.86 mW cm−2 when carbon nanowire radius, carbon loading and Pt loading are set at 45 nm, 2.0 mg cm−2 and 1.6 mg cm−2, respectively. This work is instructive to develop high-performance fuel cell electrodes with high catalyst utilization as well as electrodes of other electrochemical energy conversion and storage devices.