Direct Formic Acid Fuel Cell Anode Catalyst Layer: Enhanced Mass Transport with Increased Porosity

Abstract

Batteries are the predominant portable power source, but are inefficient due to their limited charge capacity, lengthy recharging times, and exponential degradation. Direct formic acid fuel cells present a sustainable replacement to batteries with their instantaneous refueling times and high efficiency. However, small pore size (~20 nm) between the agglomerates in the anode catalyst layer and two-phase flow hinders the mass transport and reduces the cell performance. Therefore, enhancing the cell performance also requires the two-phase flow optimization of the liquid reactant (formic acid, HCOOH) and gaseous product (carbon dioxide, CO2). To accomplish this, pore-forming agent (magnesium oxide, MgO) was incorporated during the anode catalyst layer fabrication and subsequent removal leaving behind lager pores to improve the two-phase flow through the anode catalyst layer.In 2012, the addition and subsequent removal of pore-former (lithium carbonate, LiCO3), formed ~10 μm pores within the anode catalyst layer.[1] The optimal performance was found for pores formed from with 17.5 wt% LiCO3; however, the formic acid electrooxidation charge transfer activity was reduced, due to the size of the pore-former increased the separation of the agglomerates and reduced the connected electrochemical surface area.To avoid damaging the integrity of the anode catalyst layer, previous work to integrate a smaller pore-former MgO (~50 nm), into the anode catalyst layer was investigated. [2] Compared to an anode catalyst layer without pore-former, 25 wt% pore-former increased the electrochemical surface area and cell performance by 293% and 86%, respectfully. The present study aims to further explore varying wt% of pore-former with additional sonication of the catalyst/ionomer ink prior to fabrication. The uniformity and effect of agglomerate size vs. MgO addition will be explored by quantifying the viscosity of the catalyst ink. [3] Bauskar, A.S. and Rice, C.A., Impact of Anode Catalyst Layer Porosity on the Performance of a Direct Formic Acid Fuel cell. 2012, 62, 36-41.Lam, S., Bixby, M.M., and Rice, C.A., Optimization of Mass Transport within Direct Formic Acid Fuel Cell Catalyst Layer via Pore Formers.Khandavalli, S., Park, H.J., Kariuki, N.N., Myers, J.D., Stickel, J.J., Hurst, K., Neyerlin, C.K., Ulsh, M., and Mauger, A.S., Rheological Investigation on the Microstucture of Fuel Cell Catalyst Inks. 2018, 10, 50.