Enhancing pH-gradient microscale bipolar interfaces (PMBI) enabled direct methanol hydrogen peroxide fuel cell (DMHPFC) performance under varying operating conditions

Abstract

This study introduces a direct methanol hydrogen peroxide fuel cell (DMHPFC) using a pH-gradient-enabled microscale bipolar interface (PMBI) to address limitations in direct methanol fuel cells (DMFCs). Unlike conventional fuel cells that use oxygen, the DMHPFC utilizes H₂O₂, enhancing reactant availability and reaction kinetics. The PMBI maintains separate pH environments at the anode and cathode. The PMBI-DMHPFC combines an alkaline anode for methanol oxidation and an acidic cathode for hydrogen peroxide reduction, achieving a theoretical open-circuit voltage (OCV) of 1.72 V (compared to a theoretical OCV of 1.25 V for DMFCs) and a volumetric energy density of 9.2 kWh l⁻¹ using aqueous methanol (39% vol) and hydrogen peroxide (41% vol). This energy density quadruples that of compressed hydrogen (2.1 kWh l⁻¹ at 69 MPa). This study identifies optimal operating conditions: 5 M methanol with 3 M KOH as anolyte, 5 M hydrogen peroxide with 1.5 M sulfuric acid as catholyte, Nafion 115 (127 μm) as membrane, and flow rate of 2.5 ml min⁻¹ cm⁻² – that maximize the power output and minimize activation-, ohmic- and mass transfer losses in DMHPFCs. Performance evaluation reveals a measured OCV of 1.69 V. While the PMBI-DMHPFC surpasses DMFC performance, its high OCV and energy density are not fully translated into high power density due to significantly higher activation and mass transport losses compared to H₂–O₂ fuel cells, which typically achieve peak power densities above 1000 mW cm⁻². The DMHPFC achieves a peak power density of 630 mW cm⁻² at the unusually high voltage of 0.8 V, reflecting the unique PMBI design and optimized operating conditions that reduce losses. This steeper voltage drop is attributed to sluggish reaction kinetics, membrane crossover and mass transport limitations. It highlights the potential for improved performance through advanced electrocatalysts, optimized membrane materials and flow design from this promising baseline.