Efficient gas diffusion electrodes supported on nanoporous polycarbonate membranes for application in micro-fuel cells

JOSE LUIS FERNANDEZ; JUSTO D. MOLINA

Mar del Plata

Congreso; 34th Topical Meeting of the International Society of Electrochemistry; 2023

International Society of Electrochemistry (ISE)

Portable energy sources are essential technological components in modern life, which explains the considerable efforts that are being directed toward the development of portable devices able to fit in a sustainable scheme of energy distribution. Over this line, energy-conversion micro-devices based on the technology of low-temperature fuel cells, known as micro-fuel cells (µFCs), are being considered as a viable alternative complementing other power sources such as rechargeable batteries. The conceptual idea beneath the µFCs is to attain an efficient and well-controlled fuel oxidation process, e.g. through hydrogen oxidation (hor) and oxygen reduction (orr) in hydrogen-µFCs (H-µFCs), on a very confined electrode-electrolyte arrangement that optimizes the design of the reaction place. Moreover, these micro-cells are interconnected along a narrowed volume with the assistance of microfabrication techniques in order to reach the desired power. In this configuration, the design of the gas diffusion electrode (GDE) both for the cathode and also for the anode in H-µFCs is critical, as it must guarantee an efficient arrival of the reactant (O2 or H2) and removal of products (H2O, H+) to/from the electrocatalyst surface, as well as a low contact resistance and an acceptable long-time stability. In this context, this work describes the fabrication of GDEs whose configuration can be easily adapted for implementation as electrodes in membrane-less H-µFCs. For fabrication of these GDEs, track-etched nanoporous polycarbonate membranes (NPCM) are used as a template to take advantage of their porous structure for defining a well-controlled catalyst/electrolyte/gas reactant interface, and as a support to provide flexibility and mechanical stability to the GDE. A catalyst layer (sputtered Pt) and a Nafion® film are deposited on the NPCMs. Schemes in Fig. 1 illustrate two analyzed configurations, which only differ in the order of these two layers. In configuration (a), the Pt layer is deposited right onto the NPCM surface, and a thin Nafion® layer containing Vulcan carbon (to improve electron conductivity) covers this Pt film. In this case, the uncovered surfaces of the NPCMs are etched with oxygen plasma to favor the percolation of electrolyte toward the Pt surface. The hydrophobic nature of the Nafion® layer avoids the electrolyte passing through, and provides a quite thin barrier for the gas reactant to dissolve and diffuse toward the reaction place. On the other hand, in configuration (b) the thin Nafion® layer lays over the naked NPCMs, and Pt is sputtered on top of this layer. In this case the catalyst is almost in direct contact with the gas reactant, and connects with the electrolyte through the hydrophilic ionic-conductive Nafion® pores. The performances of these configurations as GDEs for the hor and orr in acid electrolyte were evaluated by cyclic voltammetry and steady-state polarization curves measured by application of potential steps. Figs. 2-a and 2-b show typical voltammetric and steady-state responses, where it is possible to check the large limiting current densities (> 0.3 A cm-2 for the hor) that can be attained with these two configurations (due to the optimized transport of dissolved gas reactant), verifying acceptable stability and contact resistance (much lower in configuration b). In conclusion, these NPCM-based GDEs presented good enough performances to be considered as potential components for H-µFCs.