Performance characteristics of a passive direct formate fuel cell

Abstract

Summary A passive direct formate fuel cell using ambient air is designed, fabricated, and tested. This fuel cell does not use any auxiliary devices such as pumps, gas compressors, and gas blowers. The simple and compact structure well fits the need of portable applications. In this fuel cell, a solution having formate and alkali is anode fuel, while ambient oxygen is used as cathode oxidant, and a cation exchange membrane serves as an ionic conductor between two electrodes. Our performance tests have shown that a peak power density of 16.6 mW cm−2 as well as an open‐circuit voltage of 0.97 V are achieved by the present fuel cell at 60 °C, when running on anode fuel containing 5.0 M sodium formate and 3.0 M sodium hydroxide. This performance is even 31.7% higher than that achieved by an active direct formate fuel cell reported in the open literature (12.6 mW cm−2), which also uses a cation exchange membrane. The effects of the operating parameters are also investigated, including the concentrations of fuel and alkali as well as the operating temperature. The fuel solution at low concentrations results in an inadequate local concentration of reactants, so that the anodic kinetics becomes sluggish. Although increasing the sodium hydroxide concentration enhances the anodic formate oxidation kinetics, too high concentration of sodium hydroxide leads to too many active sites being covered by hydroxide ions and thus adsorption and reaction of formate ions being limited. Moreover, too high concentration of sodium hydroxide or sodium formate also leads to the fuel solution being highly viscous, hindering the motion of various ions, as well as thus increasing both concentration loss and the ohmic loss. The compromise between benefits and the drawbacks of using high‐concentration reactants results in an optimal composition of the fuel solution, which contains 5.0 M sodium formate and 3.0 M sodium hydroxide. Furthermore, the present fuel cell delivers a voltage around 0.6 V for 20 hours at 4.0 mA cm−2.

Influence of Nafion loading in the anode catalyst layer on the performance of anion‐exchange membrane direct formate fuel cells

“…Compared to other scenarios with HCOOK concentrations greater than 1 M, the mass transport overpotential appears to be very strong, resulting in a low limiting current density. Therefore, the adsorption of HCOOK on the active sites is anticipated to become insufficient for high OH À concentration coverage of the active sites, 19,25 resulting in the low limiting current density of the AEM DFFCs supplied with relatively dilute fuel, say 1 M.…”

“…The pretreatment Nafion membrane, in particular, is capable of serving as a cation-exchange membrane for transporting cations such as sodium or potassium ions from the anode to the cathode of alkaline-acid DFFCs. [21][22][23][24][25] After determining the DFFC membrane, a suitable ionomer polymer, which is required to keep the discrete catalyst particle in position and is extremely porous on the gas diffusion layer, must be chosen for electrode preparation. In terms of hydrophilicity, water retention, and electrode morphology, the type and content of the ionomer present in the electrode is one of the essential elements influencing mass and charge transports in fuel cells.…”

“…In general, anion-conducting ionomers such as AS4, A3, I2, and QAPSF are utilized with an AEM for DFFC, [9][10][11][12][13][14][15][16][17][18][19][20] whereas the cation-exchange Nafion ionomer is usually used as the pretreated Nafion membrane for DFFC. [21][22][23][24][25] Furthermore, several neutral polymers, such as PTFE and PVDF-HEP, were used as ionomers in the fuel cell electrode, and their performances were compared to that of the fuel cell containing an ion-conducting ionomer. 20,[26][27][28] The results consistently showed that when the fuel cells were fed with fuel solution mixed with the supporting electrolyte, fuel cells containing optimal neutral ionomer composition in the alkaline anode performed better than those containing anion-conducting ionomers.…”

Performance of Direct Formate Fuel Cell Using Non-Precious Metal Cathode Catalyst

“…Since the Pt/C catalyst showed very low tolerance toward HCOONa, the presence of HCOONa at the cathode leads to the formate oxidation reaction on the Pt surface and thus, reduced cell performance. In addition, the e ect of the crossover can be veri ed from the drop of open circuit voltage (OCV) as the HCOONa concentration increases from 2 to 4 M (Su et al, 2019). For the Fe-and Co-NCNT cathode catalyst, the optimum concentration is at 4 M HCOONa, resulting a maximum power density of 39.7 mW cm −2 and 89.8 mW cm −2 for Fe-NCNT and Co-NCNT, respectively.…”

Effects of Nafion ionomer content on the performance of membraneless direct formate fuel cells

“…Note that direct formate fuel cells (DFFCs) have recently attracted significant attention and are becoming an emerging energy technology, primarily because they use carbon-neutral fuel with low-cost electrocatalytic and membrane materials. [14][15][16][17][18][19][20] Among those studies, the low catalytic activity of Pt/C for the oxidation of potassium formate was also found in. 18 Furthermore, although numerous MFC studies have been published, only a few studies 13,14,21,22 attempted to enlarge the fuel flow field of the MFCs with more complicated fuel cell configuration to produce a higher current density.…”