[en] An air-breathing stack for a direct formic acid fuel cell (DFAFC) was designed, fabricated and evaluated. The DFAFC stack consisted of six cells arranged in a hexagonal arrangement and each single cell contained a pair of stainless steel current collectors, a membrane electrode assembly (MEA) and a cathode end-plate. A fuel reservoir was located at the center which supplied formic acid supply to the anode of each cell. The effects of fuel concentration, palladium (Pd) loading at the anode and activation on DFAFC performance and long term operation were evaluated. DFAFC stack performance increased with increasing fuel concentration and a stable power up to 200 mW at 2.4 V was achieved for passive and ambient conditions at a 7 M fuel concentration. Catalyst loading had a slight effect on DFAFC performance, where 4 mg cm-2 Pd loading was best for 7 M fuel operation. During long-term operation, the DFAFC stack could be operated for 27 hours without adding more fuel and less than a 20 % reduction in performance during operation. MEA reactivation with deionized water technique was required for immediate recovery of stack performance. (author)

[en] In the present study, we suggest a new way to reactivate performance of direct formic acid fuel cell (DFAFC) and explain its mechanism by employing electrochemical analyses like chronoamperometry (CA) and cyclic voltammogram (CV). For the evaluation of DFAFC performic, palladium (Pd) and platinum (Pt) are used as anode and cathode catalysts, respectively, and are applied to a Naf ion membrane by catalyst-coated membrane spraying. After long DFAFC operation performed at 0.2 and 0.4 V and then CV test, DFAFC performance is better than its initial performance. It is attributed to dissolution of anode Pd into Pd²⁺. By characterizations like TEM, Z-potential, CV and electrochemical impedance spectroscopy, it is evaluated that such dissolved Pd²⁺ ions lead to (1) increase in the electrochemically active surface by reduction in Pd particle size and its improved redistribution and (2) increment in the total oxidation charge by fast reaction rate of the Pd dissolution reaction

[en] This study introduces a novel nano-sized palladium complex with high electrocatalytic activity and stability as a catalyst for the anodic reaction of direct Formic acid fuel cell (DFAFC). Morphologically, as prepared Pd-complex has intersected nano-rod like structure with an average particle size of 7 nm. Nano-Pd-complex modified GC electrode showed 10 times higher electrocatalytic activity and 16 times higher stability compared with the traditional Pd nanoparticles modified GC electrode with the same Pd weight. This significant improvement may be attributed to its small size and bulky structure that hinders the sintering of the active Pd atoms (i.e., obstructs the growth of Pd particle size) and impedes the adsorption of poisoning intermediate species (e.g., CO) and/or formation reversible surface hydride as evidenced by the DFT calculations. This study introduces a new promising category of Pd-based catalyst with high activity, catalyst utilization and durability for DFAFCs applications.

[en] This study is focused on development of membrane electrode assembly (MEA) for direct formic acid fuel cell (DFAFC). The effects of the backing layer, the loading of the gas diffusion layer (GDL), the carbon structures and the electrolyte membrane types, and fuel concentrations on the DFAFC's performance are investigated. Two types of backing layer are used in either a carbon paper (CP) or carbon cloth (CC) form, and three different types of carbon structures, carbon black (CB), carbon nanofiber (CNF) and carbon nanotube (CNT), are studied. A single cell DFAFC is tested to obtain the performance of the MEA, including the open circuit potential (OCP), current density, and power density. From the results, carbon paper indicates a much better performance than carbon cloth and gas diffusion layer (GDL) with 1 mg cm^-2 loading shows a uniform surface morphology under scanning electron microscopy (SEM) and records a higher power density than 2.5 mg cm^-2. Moreover, it is found that the power density increases with increase of the formic acid concentration up to an optimum concentration. However, the optimum fuel concentrations are different for each type of carbon structure. The highest power density is obtained using a combination of CNT and electrolyte membrane of Nafion 117 at 18.36 mW cm^-2 using 10 M fuel concentration. (author)

[en] In this work, carbon supported Pt _xPd_1-x (x = 0-1) nanocatalysts were investigated for formic acid oxidation. These catalysts were synthesized by a surfactant-stabilized method with 3-(N,N-dimethyldodecylammonio) propanesulfonate (SB12) as the stabilizer. They show better Pt/Pd dispersion and higher catalytic performance than the corresponding commercial catalysts. Furthermore, the electrocatalytic properties of Pt _xPd_1-x/C were found to depend strongly on the Pt/Pd deposition sequence and on the Pt/Pd atomic ratio. At a lower potential, formic acid oxidation current on co-deposited Pt _xPd_1-x/C catalysts increase with increasing Pd surface concentration. Nanoscale Pd/C is a promising formic acid oxidation catalyst candidate for the direct formic acid fuel cell

[en] Highlights: ► Pd–Cu/C catalysts with different atomic ratios of Pd and Cu are prepared with simple method. ► All electrocatalytic performances of Pd–Cu/C for formic acid oxidation are better than that of Pd/C. ► It is due to no catalytic performance of Pd–Cu/C for decomposition of formic acid. ► Electrocatalytic performance of the Pd–Cu/C with 3:1 of Pd and Cu is best. - Abstract: The direct formic acid fuel cell (DFAFC) has two major shortcomings that limit its lifespan and performance: (i) the poor electrocatalytic stability of the carbon supported Pd (Pd/C) catalyst and (ii) rapid decomposition of formic acid over the Pd/C catalyst. To solve the problems, the carbon-supported Pd–Cu (Pd–Cu/C) catalysts with different atomic ratios of Pd and Cu are successfully prepared with a simple impregnation–reduction method. It is reported for the first time that the electrocatalytic performances of the Pd–Cu/C catalysts for formic acid oxidation are related to the decomposition rate of formic acid over the Pd–Cu/C catalysts. When the content of Cu in the Pd–Cu/C catalysts is gradually increased, the decomposition rate of formic acid over the Pd–Cu/C catalysts is correspondingly decreased, leading to the decrease in the production of poisoned CO. Therefore, the electrocatalytic performances of the Pd–Cu/C catalysts for formic acid oxidation are much better than that of the Pd/C catalyst. However, when the content of Cu in the Pd–Cu/C catalyst is too high, the electrocatalytic performance of the Pd–Cu/C catalyst would be decreased because Cu has no electrocatalytic activity for formic acid oxidation. Based on the above reasons, among all Pd–Cu/C catalysts prepared, the electrocatalytic performance of the Pd–Cu/C catalyst with 3:1 atomic ratio of Pd and Cu for formic acid oxidation is best.

[en] The storage and utilization of low-carbon electricity and decarbonization of transportation are essential components for the future energy transition into a low-carbon economy. While hydrogen has been identified as a potential energy carrier, the lack of viable technologies for safe and efficient storage and transportation of H${}_2$ greatly limits its applications and deployment at scale. Formic acid (FA) is considered one of the promising H${}_2$ energy carriers because of its high volumetric H${}_2$ storage capacity of 53 g H${}_2$/L, and relatively low toxicity and flammability for convenient and low-cost storage and transportation. FA can be employed to generate electricity either in direct FA fuel cells (FCs) or indirectly as an H${}_2$ source for hydrogen FCs. FA can enable large-scale chemical H${}_2$ storage to eliminate energy-intensive and expensive processes for H${}_2$ liquefaction and compression and thus to achieve higher efficiency and broader utilization. This perspective summarizes recent advances in catalyst development for selective dehydrogenation of FA and high-pressure H${}_2$ production. The advantages and limitations of FA-to-power options are highlighted. Existing life cycle assessment (LCA) and economic analysis studies are reviewed to discuss the feasibility and future potential of FA as a fuel. (© 2022 Wiley-VCH GmbH)

[en] Highlights: • A selective deposition-etching approach is developed for the synthesis of Pt₄PdCu_0.4 nanoframes. • The deposition locations of Pt on Pd nanocrystals can be controlled by addition of Cu(II). • Pt₄PdCu_0.4 nanoframes show enhanced performance in oxygen reduction and formic acid oxidation. • The effects of electronic and surface structures on electrocatalytic performance are elucidated. • This work sets up a platform for simultaneously tuning surface and electronic structures. The development of bifunctional electrocatalysts for direct formic acid fuel cells requires low Pt usage, high activities in both oxygen reduction reaction (ORR) and formic acid oxidation (FAO), low CO production, and high resistance to CO. It remains a grand challenge to achieve all in a single material. Here we report a copper-assisted selective deposition-etching approach to Pt₄PdCu_0.4 nanoframes that meet all the requirements, offered by structure and electronic structure effects. Impressively, the specific activities of Pt₄PdCu_0.4 nanoframes in ORR and FAO are 9.2 times and 10.2 times higher than commercial Pt/C, respectively, with excellent durability. This work provides insights into the catalyst design that one single material synthesis sets up a platform for simultaneously tuning surface and electronic structures.

[en] A Pd/WO₃/C nanocomposite with 3-aminopropyltrimethoxysilane (APTMS)-functionalized tungsten oxide nanosheets (Pd/WO₃/C-APTMS) was synthesized and applied as the efficient anode catalyst for direct formic acid fuel cells (DFAFCs). The mechanism for synthesizing the nanocomposite is as follows: initially, [PdCl₄]²⁻ was assembled onto the tungsten oxide nanosheets modified with APTMS. Following this, Pd nanoparticles were reduced via traditional impregnation reduction of [PdCl₄]²⁻ with NaBH₄. The transmission electron microscope (TEM) images revealed that the Pd nanoparticles were uniformly dispersed on WO₃ nanosheets and were approximately 2.7 nm in size. The electrochemical test results showed that enhanced electrocatalytic activity for the formic acid oxidation reaction (FAOR) was obtained on the Pd/WO₃/C catalyst compared with Pd/C. The higher electrocatalytic activity might be attributed to the uniform distribution of Pd with smaller particles. Furthermore, it is likely that the improvement in catalytic stability for the Pd/WO₃/C catalyst is due to the hydrogen spillover effect of WO₃ particles. These results indicate that this novel Pd/WO₃/C-APTMS nanocomposite exhibits promising potential for use as an anode electrocatalyst in DFAFCs.

[en] Direct formic acid fuel cells are advantageous as portable power generating devices. In the present work, an anode catalyst for direct formic acid fuel cell (DFAFC) is presented which has good catalytic activity for formic acid oxidation. The catalyst is composed of Pd and conducting polymer polyaniline (Pd-PANI) nanocomposite. The catalyst was prepared by using a single step galvanostatic electrochemical deposition method. The Pd-PANI catalyst was electrodeposited at different time durations and a comparison of the catalytic activity at each deposition time was carried out and optimized. (paper)