阳极流道具有微孔阵列的被动式纸基微流体燃料电池性能特性

Cell performance of passive paper-based microfluidic fuel cells with mini-hole array in the anode flow channel

纸基微流体燃料电池利用纸多孔介质内毛细渗流实现了阴阳极反应物被动输运和自然分隔,去除了质子交换膜和微泵,是基于电化学反应的新一代纸基微流控芯片理想的新型微型电源.针对常规纸基微流体燃料电池存在的燃料传质限制,本文提出阳极流道具有微孔阵列的新型电池结构,利用微孔阵列强化燃料的对流/扩散传质提高电池性能,研究了阴阳极间距、电极长度、燃料浓度及电解液浓度对电池性能特性的影响.研究结果表明,阳极流道内微孔阵列能够强化燃料传质并降低离子传输阻力,使得阳极流道具有微孔阵列的纸基微流体燃料电池最大功率密度提高41.2%;减少阴阳极间距有利于降低离子传输阻力,而且阴极电解液流速大于阳极电解液流速,抑制了燃料渗透,使得电池性能提升;电池性能随燃料和电解液浓度上升先升高后降低.当阴阳极间距为1.0 mm,电极长度为5.0 mm,燃料和电解液浓度均为2.0 mol/L时,电池性能达到最优,其最大功率密度为29.7 mW/cm^2.

Paper-based microfluidic fuel cells(PMFCs)exploit the capillary flow in paper porous media to enable passive transport of reactants,and also use the co-laminar flow nature to separate the fuel and oxidant,thereby eliminating the conventional proton exchange membrane and micro-pumps.PMFCs have been regarded as promising micro-power sources for nextgeneration paper-based electrochemical microfluidic assay for biomedical diagnosis.The PMFC performance is usually limited by fuel transport,failing to meet the power requirement.At present,the paperbased microfluidic fuel cells have been reported to improve the performance mainly by changing the operating parameters,the physical parameters of the paper channel and the absorption pad,and the cell structure.However,few studies have been reported to improve the cell performance by enhancing fuel transfer.In this paper,a new anode structure is proposed to enhance fuel transfer.That is,a mini-hole array is constructed in the paper-based channel on the anode to make part of the catalyst layer of the anode contact with the mini-hole array.It was expected that the fluid in the mini-hole array can not only enhance the convective fuel transport,but also improve the diffusive fuel transport due to the direct contact between the fluid in the paper-based flow channel and anode catalyst layer.Performance comparison was firstly conducted between paper-based microfluidic fuel cells with conventional flow channel and mini-hole array in the anode flow channel.Moreover,effects of operation conditions including anode/cathode interspace,electrode length,fuel and electrolyte concentration on the cell performance were investigated and discussed.The experimental results confirmed that the mini-hole array in the anode flow channel can enhance fuel transport and ion conduction.As compared to the PMFC with the conventional flow channel,the PMFC with mini-hole array in the anode flow channel yielded 41.2%higher maximum power density.In addition,the experimental data also indicated that the ion transfer resistance can be reduced by diminishing the anode/cathode interspace,leading to an improved cell performance.No obvious fuel crossover was observed even at the interspace of 1.0 mm,because the flow rate of catholyte was higher than that of the anolyte,impeding the fuel crossover towards the cathode.The maximum power density of the cell increased with the decrease in the electrode length.This was mainly due to electrochemical reaction consumption and slow diffusion on the anode surface,which would reduce the fuel concentration on the anode surface along the flow direction,forming a concentration boundary layer and limiting the cell performance.In addition,upon the increasement of fuel or electrolyte concentration,the cell performance was enhanced at relatively low concentration but then dropped at high concentration.The fuel transfer was enhanced at high concentration and the ion transfer resistance can be reduced by increasing the electrolyte concentration,leading to an improved cell performance.However,the viscosity and density of the fuel and electrolyte increase with the electrolyte concentration,which led to the decrease of the flow rate of the reactants,further resulting in fuel mass transfer limitation and performance reduction.The optimal power density reached 29.7 m W/cm^2 by the proposed PMFC at the anode/cathode interspace of 1.0 mm,the electrode length of 5.0 mm,and the fuel and electrolyte concentrations of 2.0 mol/L.