Direct Formic Acid Fuel Cell Research Articles

Synergistic enhancement of formic acid electro-oxidation on PtxCuy co-electrodeposited binary catalysts

A propitious binary catalyst composed of Pt and Cu which were electrodeposited simultaneously onto a glassy carbon (GC) substrate was recommended for the formic acid (FA) electro-oxidation reaction (FAOR); the principal anodic reaction in the direct FA fuel cells (DFAFCs). The simultaneous co-electrodeposition of Pt and Cu in the catalyst provided an opportunity to tune the geometric functionality of the catalyst to resist the adsorption of poisoning CO at the Pt surface that represented the major impediment for DFAFCs marketing. The catalytic activity of the catalyst toward FAOR was significantly influenced by the (Pt4+/Cu2+) molar ratio of the electrolyte during electrodeposition, which also affected the surface coverage of Pt and Cu in the catalyst. Interestingly, with a molar (Pt4+/Cu2+) ratio of (1:4), the catalyst sustained superior (3.58 compared to 0.65 obtained at the pristine Pt/GC catalyst) activity for FAOR, concurrently with up to four-times (0.73 compared to 0.18 obtained at the pristine Pt/GC catalyst) improvement in the catalytic tolerance against CO poisoning. This associated, surprisingly, a negative shift of ca. 336 mV in the onset potential of FAOR, in an indication for the competitiveness of the catalyst to minimize superfluous polarizations in DFAFCs. Furthermore, it offered a better (ended up with 20% loss in the activity) stability for continuous (1 h) electrolysis than pristine Pt/GC catalyst (the loss reached 35%). The impedance and CO stripping measurements together excluded the electronic element but confirmed the geometrical influence in the catalytic enhancement.

Electrocatalytic oxidation of formic acid on Pd/CNTs nanocatalysts synthesized in special “non-aqueous” system

It remains a major challenge to enhance the activity of Pd catalyst and meanwhile minimize the CO poisoning due to adsorbed CO during formic acid oxidation (FAO). Herein, highly dispersed Pd on multi-walled carbon nanotubes (MWCNTs) supported catalysts were prepared in a non-aqueous deep eutectic solvent (DES) system. The catalyst prepared at 170 °C (referred to Pd/CNTs-D170) showed higher catalytic performance toward FAO (peak current: 1712.6 mA mgPd−1) and better CO anti-poisoning capability (onset potential: 0.59 V, peak potential: 0.69 V) than the Pd/CNTs-W (synthesized in water) (1130.9 mA mgPd−1, 0.65 V, 0.71 V) and commercial Pd/C (555.8 mA mgPd−1, 0.66 V, 0.74 V) catalysts. This study provides a suitable strategy for the preparation of high-performance Pd-based electrocatalysts for direct formic acid fuel cell (DFAFC).

Porous palladium phosphide nanotubes for formic acid electrooxidation

AbstractThe development of an efficient catalyst for formic acid electrocatalytic oxidation reaction (FAEOR) is of great significance to accelerate the commercial application of direct formic acid fuel cells (DFAFC). Herein, palladium phosphide (PdxPy) porous nanotubes (PNTs) with different phosphide content (i.e., Pd3P and Pd5P2) are prepared by combining the self‐template reduction method of dimethylglyoxime‐Pd(II) complex nanorods and succedent phosphating treatment. During the reduction process, the self‐removal of the template and the continual inside–outside Ostwald ripening phenomenon are responsible for the generation of the one‐dimensional hollow and porous architecture. On the basis of the unique synthetic procedure and structural advantages, Pd3P PNTs with optimized phosphide content show outstanding electroactivity and stability for FAEOR. Importantly, the strong electronic effect between Pd and P promotes the direct pathway of FAEOR and inhibits the occurrence of the formic acid decomposition reaction, which effectively enhances the FAEOR electroactivity of Pd3P PNTs. In view of the facial synthesis, excellent electroactivity, high stability, and unordinary selectivity, Pd3P PNTs have the potential to be an efficient anode electrocatalyst for DFAFC.

Porous Electrodes from Self-Assembled 3d Jointed Pd Polyhedra for Direct Formic Acid Fuel Cells

Porous Electrodes from Self-Assembled 3d Jointed Pd Polyhedra for Direct Formic Acid Fuel Cells

Surface engineering of nanotubular ferric oxyhydroxide “goethite” on platinum anodes for durable formic acid fuel cells

A peerless inexpensive electrochemical engineering of spherical Pt nanoparticles (nano-Pt: ca. 100 nm in average diameter) was achieved with intersected ferric oxyhydroxide nanotubes (α-FeOOH (goethite): ca. 20 nm in average diameter). The FeOOH@Pt catalyst exhibited ca. 2.5 and 1.94-times increases in the catalytic activity and poisoning tolerance, respectively, of the formic acid electro−oxidation (FAO) – the anodic reaction in the direct formic acid fuel cells (DFAFCs). Surprisingly, with a post-activation of the FeOOH@Pt catalyst at 0.48 V vs. reversible hydrogen electrode (RHE) in 0.2 mol L−1 NaOH, a favorable Fe2+/Fe3+ transformation succeeded to eliminate the permanent CO poisoning of Pt that impaired the catalytic performance of DFAFCs. This was synchronized (relatively to nano-Pt) with a four-fold increase in the catalytic efficiency, ca. −174 mV shift in the onset potential, and eightfold enhancement in the catalyst's durability for FAO. The activated FeOOH@Pt catalyst also showed a mass activity of 296 mA mg−1Pt (at 0.8 V), which was ca. nine times higher than that (34 mA mg−1Pt) of the commercial Pt/C catalyst. The ascertained improvement in the electron transfer at the FeOOH@Pt surface foresees quick industrialization for DFAFCs.

Synthesis of Palladium–Tungsten Metallene-Constructed Sandwich-Like Nanosheets as Bifunctional Catalysts for Direct Formic Acid Fuel Cells

Synthesis of Palladium–Tungsten Metallene-Constructed Sandwich-Like Nanosheets as Bifunctional Catalysts for Direct Formic Acid Fuel Cells

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

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.

Boosted performance of NiOx/Pt nanocatalyst for the electro-oxidation of formic acid: A substrate's functionalization with multi-walled carbon nanotubes

A novel NiOx/Pt on “mutli-wall” carbon nanotubes nanocatalyst is recommended for efficient electro-oxidation of formic acid (EOFA), the principal anodic reaction in the direct formic acid fuel cells (DFAFCs). At the NiOx/Pt/CNTs/GC catalyst, EOFA tuned the typical dual (direct/indirect) pathway mechanism (left image) to the single direct pathway mechanism (right image); overcoming efficiently the CO poisoning. • A propitious CNTs-amended NiOx/Pt nanoanode was fabricated. • It showed a promising catalytic activity toward the formic acid electro-oxidation. • The reaction proceeded exclusively via the desirable dehydrogenation pathway. • A complete suppression of the undesirable poisoning dehydration route was obtained. • Electronic and geometric enhancements were elucidated and quantified. A NiOx/Pt nanostructured catalyst was developed on a glassy carbon substrate that was functionalized with “mutli-walled” carbon nanotubes (CNTs) for the electro-oxidation of formic acid (EOFA); the essential oxidation reaction in the direct formic acid fuel cells (DFAFCs). The sequential deposition technique was adapted for the electrodeposition of platinum (n-Pt) and nickel oxide (n-NiOx) nanoparticles onto a CNTs-functionalized glassy carbon (GC) substrate. The presence of CNTs in the catalyst restricted the deposition of n-Pt and n-NiOx mostly onto their walls. Interestingly, this NiOx/Pt/CNTs/GC catalyst displayed a significant enhancement in the catalytic activity toward EOFA. This occurred by driving the reaction mechanism exclusively via the desirable direct dehydrogenation pathway with a large (−116 mV) shift (relative to that of the Pt/GC catalyst) in the onset potential with a complete suppression for the undesirable poisoning dehydration route. It also offered a much (up to 5-fold) better tolerance against the CO poisoning that normally deteriorates the performance of the DFAFCs. The electrochemical impedance spectroscopy and the Tafel representations agreed on the effective role of n-NiOx in improving the electronic properties of Pt at the surface. On parallel, an oxidative stripping voltammetry of CO from the NiOx/Pt/CNTs/GC catalyst confirmed the potential geometrical influence of CNTs in the divergence of n-Pt that mitigated the CO poisoning.

Pd Nanoparticle Size Effect of Anodic Catalysts on Direct Formic Acid Fuel Cell Initial Performance: Development of a Mathematical Model and Comparison with Experimental Results

AbstractDirect Formic Acid Fuel Cell (DFAFC) is considered as a promising liquid fuel cell. Here, the effect of palladium particle size (dPd) of anodic DFAFC catalysts on initial power density was studied. The number of electrochemically available Pd atoms on the surface of Pd nanocrystallites in the anodes were determined experimentally. The cathode potential as a function of the current density has been measured. The mathematical model describing the effect of dPd on DFAFC performance has been developed. It was assumed that: (i) Pd crystallites have shape of cuboctahedron, (ii) Pd atoms lying on edges and corners are inactive, (iii) The activity of Pd atoms lying on crystallite (111) and (100) facets do not change with dPd. The mathematical model describes well the effect of current density and dPd on fuel cell voltage and power density. The model predicts that maximum power density is reached at dPd=2.4 nm.

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

This study reports on direct formate fuel cell (DFFC) operation using non-precious metal (NPM) as the cathode catalyst. Iron- and cobalt-nitrogen-doped carbon nanotube (Fe-NCNT and Co-NCNT) were synthesized by pyrolysis of multiwalled carbon nanotubes, metal precursor and nitrogen precursor. These NPM catalysts showed high fuel tolerance in acidic medium, but the fuel tolerance in alkaline medium remains unclear. Herein, we determine the formate tolerance on the NPM catalysts and commercial Pt/C catalyst in alkaline medium. The DFFC performance test was conducted and the results compared with the direct formic acid fuel cell (DFAFC) reported in our previous work. The oxygen reduction reaction (ORR) activity and the formate tolerance on the NPM catalysts were evaluated by rotating disk electrode (RDE) in alkaline medium. Both NPM catalysts showed lower ORR activity than the Pt/C catalyst, but they exhibited higher formate tolerance than the Pt/C catalyst. Comparing the single-cell performance under various HCOONa concentrations, DFFC with Co-NCNT catalyst showed higher maximum power density than with Pt/C catalyst with 2 M KOH containing 4 M and 6 M HCOONa due to its higher formate tolerance. Therefore, it is considered that the NPM cathode is available for high concentration operation of DFFC. However, DFFC with Fe-NCNT and Co-NCNT cathode catalyst exhibited the highest maximum power density of 39.7 mW cm−2 and 89.8 mW cm−2, respectively, at 60°C with optimal fuel concentration, i.e. 2 M KOH containing 4 M HCOONa. These performances were lower than that of DFFC with Pt/C cathode catalyst at optimal fuel concentration, i.e. 2 M KOH containing 2M HCOONa. Considering the fact that the power density of DFAFC (acidic condition) using NPM catalyst was higher than that with Pt/C catalyst at optimum fuel concentration, the NPM catalysts are more preferable for the acidic condition than the alkaline condition.

Remarkable activity of a ZnPdPt anode catalyst: Synthesis, characterization, and formic acid fuel cell performance

Herein, multi-walled carbon nanotube (MWCNT) supported Zn–Pd and Zn–Pd–Pt catalysts have been prepared utilizing a sequential sodium borohydride (SBH) reduction method. The resulting Zn/MWCNT, Zn–Pd/MWCNT, and Zn–Pd–Pt/MWCNT catalysts were characterized using advanced surface analytical techniques such as X-ray diffraction (XRD), high contrast transmission electron microscopy (C-TEM), and X-ray photoelectron spectroscopy (XPS). The characterization results indicate that the Zn/MWCNT, Zn–Pd/MWCNT, and Zn–Pd–Pt/MWCNT catalysts were successfully prepared. It was observed that Pd and Pt incorporation into Zn alters the electronic structure of Zn. Cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) were used to examine the electrochemical activity of the catalysts toward the electrooxidation of formic acid (FA). The results reveal that ZnPdPt/MWCNT has a specific activity of 12.6 mA/cm2 and an electrochemical active surface area (ECSA) of 41.1 m2/g. This catalyst shows high activity, stability, and resistance when compared to Pd/MWCNT and ZnPd/MWCNT. Direct FA fuel cell (DFAFC) measurements were performed at 18–60 °C for the ZnPd/MWCNT and ZnPdPt/MWCNT catalysts. The specific activity of ZnPdPt/MWCNT was 1.45 times greater than that measured for ZnPd/MWCNT. ZnPdPt/MWCNT is a promising catalyst according to our CV, CA, EIS, and DFAFC measurements.

Conversion of Pt nanoparticles encapsulated within MIL-101(Fe) to FePt intermetallic nanoparticles supported on carbon promotes formic acid electrooxidation

Pt-based catalysts have limited usefulness in direct formic acid fuel cells (DFAFCs) due to their susceptibility to CO poisoning. Combining Pt with Fe atoms is an effective approach for suppressing Pt poisoning by CO. In this work, we fabricate novel carbon-supported FePt alloy nanoparticles (FePt@C) by pyrolyzing Pt nanoparticles encapsulated within mesoporous MIL-101(Fe) (Pt@MIL-101(Fe)). The resulting FePt nanoparticles (Fe3Pt (111)) possess a lower CO adsorption energy (0.64 eV) than the (111) surfaces of Pt, indicating that the FePt nanoparticles are far less susceptible to CO poisoning. The mass activity and current density of a 9.6 wt% FePt@C catalyst are 4.2 and 4.5 times, respectively, higher than those of a commercial Pt/C catalyst. Furthermore, the 9.6 wt% FePt@C catalyst exhibits excellent durability, with only a 0.1% loss of mass activity after 1000 cycles. These results should guide the development of improved anode catalysts for DFAFCs based on MOF precursors.

Superior formic acid electrooxidation activity on carbon nanotube‐supported binary Pd nanocatalysts prepared via sequential sodium borohydride reduction technique

In this study, multiwalled carbon nanotube (MWCNT)‐supported M (Pd, Ni, Co, Mn, V, Zn)/MWCNT monometallic and M (Ni, Co, Zn, V, Ag, Mn)@(Pd/MWCNT) binary nanocatalysts were investigated to examine the effect of second metal promotion to Pd on formic acid electrooxidation (FAEO) activity. The sequential sodium borohydride (SBH) reduction technique was used for the preparation of nanocatalysts. For binary nanocatalysts, first of all, the monometallic Pd/MWCNT nanocatalyst was prepared. Then, second metal precursors (NiCI2, CoCl2, ZnCI2, V2O5, AgNO3, and MnCI2) were added to Pd/MWCNT and further reduced with NaBH4. After filtration and drying, binary nanocatalysts M@(Pd/MWCNT) were obtained. X‐ray diffractometry (XRD), inductively coupled plasma mass spectrometer (ICP‐MS), transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS) methods were used to characterize the obtained nanocatalysts. In addition, cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements were utilized to examine the electrochemical activities of the nanocatalysts for FAEO. The results indicate that Ni@(Pd/MWCNT) nanocatalyst is better than the other nanocatalysts with 10.75‐mA cm−2 specific and 2924.48‐mA mg−1 Pd mass activity. Furthermore, Ni@(Pd/MWCNT) nanocatalyst has 110.4‐m2 g−1 electrochemical active surface area (ECSA). Consequently, it is clear that Ni@(Pd/MWCNT) nanocatalyst is a promising nanocatalyst for direct formic acid fuel cells (DFAFCs).

A “special” anhydrous system for the preparation of alloyed Pd1Ce0.5 nanonetworks catalyst supported on carbon nanotubes with high electrochemical oxidation activity for formic acid

Herein, Pd1Ce0.5 alloy nanonetworks (ANNs) on multi-walled carbon nanotubes (MWCNTs) supported bimetallic catalyst (referred to Pd1Ce0.5/MWCNTs-D) was prepared in deep eutectic solvents (DESs). The Pd1Ce0.5/MWCNTs-D catalyst shows remarkable catalytic performance toward formic acid oxidation (FAO) (1968.5 mA mgPd−1) and better CO anti-poisoning capability compare with Pd/MWCNTs-D, Pd/MWCNTs-W (prepared in water) and commercial Pd/C catalysts. The excellent network structure and synergistic effect are the main reasons for the improvement of electrochemical activity of Pd1Ce0.5/MWCNTs-D catalyst. This study provides a new method for preparation of high performance Pd-based electrocatalysts for direct formic acid fuel cell (DFAFC) applications.

Formic acid synthesis and utilization for solar energy storage through solar‐driven chloralkali process and fuel cells

AbstractThe objective of this work is to propose an integrated system for formic acid synthesis via photovoltaic (PV) assisted‐chloralkali process and clean power generation by the fuel cell. The initial step is to develop process flow diagrams and to apply heat integration techniques to conserve energy in the synthesis of formic acid and direct formic acid fuel cell (DFAFC). The proposed system forms formic acid from gaseous H2 produced from chloralkali unit and captured CO2. The electricity requirements of both PV‐assisted chloralkali and compression stages are supplied from the PV units. The results imply that the chloralkali process necessitates about 7.22 MW power to produce hydrogen at 25°C and 1 bar with an energy efficiency of 84%. H2 and CO2 gases are compressed to 60 bars with a total energy requirement of 951 kW. In the heat integration part, different scenarios are developed to determine the minimum heating and cooling requirements for maximum heat recovery. The results of such heat integration were achieved to conserve the energy in the formic acid process with total hot and cold utilities of 599 kW and 1884 kW, respectively.

Investigation on a Novel Direct Liquid Fuel Cell Feeding on Oxalyl Dihydrazide

Direct liquid fuel cells (DLFCs) are promising candidates for portable applications, because they have high energy density which means long runtime, high energy efficiency, and don’t require time-consuming recharging. At present, several types of DLFCs have been invented such as Direct Methanol Fuel Cells (DMFCs), Direct Formic Acid Fuel Cells (DFAFCs), Direct Sodium Borohydride Fuel Cells (DSBFCs), Direct Hydrazine Fuel Cells (DHFCs) and so on. In this work, we propose a novel direct liquid fuel cell feeding on oxalyl dihydrazide which presents as solid power at room temperature and can be easily dissolved in alkali solution, without any emitting toxic gases. Several potential anode catalysts such as Pt/C, PtRu/C and Au/C are evaluated using a three-electrode cell. The results show that Pt/C is more suitable for the electrochemical oxidation of oxalyl dihydrazide than PtRu/C and Au/C. Using Pt/C as anode catalyst, we designed and fabricated two types of Membrane Electrode Assemblies (MEAs) of different structure, one-catalyst-layer MEA (MEA-1CL) and two-catalyst-layer MEA (MEA-2CL). The single cell tests show MEA-2CL obtain higher I–V performance.

Carbon-Supported Single-Atom Catalysts for Formic Acid Oxidation and Oxygen Reduction Reactions.

The commercialization of fuel cells, especially for direct formic acid fuel cells (DFAFCs) and proton-exchange membrane fuel cells (PEMFCs), is significantly restrained by the high cost, poor stability, and sluggish kinetics of platinum group metals (PGM) catalysts for both the anodic formic acid oxidation reaction (FAOR) and the cathodic oxygen reduction reaction (ORR). Currently, it has confronted with challenges, including exploring highly active, cost-effective, and stable catalysts to replace PGM for DFAFCs and PEMFCs. Recently, the increasing investigation has been focused on the single-atom catalysts (SACs) to enhance the catalytic performance owing to the maximum atom utilization and highly exposed active sites. The aim of this review is to present the recent research activities on carbon supported SACs. At the beginning of the review, metal-based SACs supported on different carbon supports, and the typical characterization methods are introduced. Subsequently, recent advances in metal-based SACs for FAOR and ORR catalysis are scientifically summarized. Particularly, some representative metal-based SACs for ORR activity are further exemplified with a deeper understanding of structure-activity relationships. Finally, the challenges and opportunities of SACs are prospected, such as the mechanism understanding and commercial applications.

Mechanistic effects of blending formic acid with ethanol on Pd activity towards formic acid oxidation in acidic media.

The direct formic acid fuel cell (DFAFC) is one of the most promising direct liquid fuel cells. Pd is the most active catalyst towards formic oxidation, however, it suffers from CO-like poisoning and instability in acidic media. Blending formic acid with ethanol is known to synergistically enhance the Pt catalytic activity of Pt. However, it has not been studied in the case of Pd. In this study, ethanol/formic acid blends were tested, aiming at understanding the effect of ethanol on the formic acid oxidation mechanism at Pd and how the direct and indirect pathways could be affected. The blends consisted of different formic acid (up to 4 M) and ethanol (up to 0.5 M) concentrations. The catalytic activity of a 40% Pd/C catalyst was tested in 0.1 M H2SO4 + XFA + YEtOH using cyclic voltammetry, while the catalyst resistance to poisoning in the presence and absence of ethanol was tested using chronopotentiometry. The use of these blends is found to not only eliminate the indirect pathway but also slowly decrease the direct pathway activity too. That is believed to be due to the different ethanol adsorption orientations at different potentials. This study should open the door for further studying the oxidation of FA/ethanol blends using different pHs and different Pd-based catalysts.

PdAg Nanoparticles with Different Sizes: Facile One-Step Synthesis and High Electrocatalytic Activity for Formic Acid Oxidation.

Recently, direct formic acid fuel cells (DFAFCs) which possess superior advantages such as a low operating temperature, light environmental pollution and high energy density, have been considered as one of the power generation technologies with a bright prospect. Herein, bimetallic PdAg nanoparticles (NPs) with different particle sizes were successfully produced via an easy one-pot solvothermal co-reduction synthetic route and their electrocatalytic performance for formic acid oxidation (FAO) were further investigated. In our strategy, the size of PdAg NPs can be easily controlled by only varying the concentration of precursors. The larger sized PdAg alloy (9.5 nm, noted as PdAg-L) was obtained at a low concentration of precursors, while the smaller PdAg alloy (3.7 nm, named as PdAg-S) was separated from the reaction system with higher solubility by centrifugation. The electrocatalytic activity and stability of the obtained PdAg NPs could be well optimized when incorporated with carbon (C), which is owing to a synergetic effect. The PdAg-S/C exhibits the highest mass activity with around 1.6 times that of PdAg-L/C and 2 times that of commercial Pd/C, which can be attributed to its larger ECSA and lower adsorption energy of the intermediate to facilitate the direct oxidation of HCOOH molecule.

Effect of the Pore Structure of the Gas Diffusion Electrode on the Power Generation and Mass Transport Properties of Direct Formic Acid Fuel Cell

Direct Formic Acid Fuel Cell has been attracted match attention due to its higher power density and lower crossover. In order to improve their performance, we have tried to improve the mass transport in the anode electrode since a large amount of carbon dioxide is emitted by the electrochemical reaction. For the anode electrode, diffusion layer, such as carbon cloth and carbon paper used in the polymer electrolyte fuel cell, is commonly used in direct formic acid fuel cell. These diffusion layers were suitable for the gas supplying; however, it is not clear that these diffusion layers were also suitable for direct liquid fuel cell using liquid fuel. Moreover, the suitable pore structure of diffusion layer for the direct liquid fuel cell is also unknown. In this context, we fabricated the gas diffusion layer having different pore diameter, thickness and porosity using same manner and material in order to evaluate the effect of the pore structure of diffusion layers on the power generation characteristics and mass transport properties in direct formic acid fuel cell. The diffusion layers having 0.03-0.1 mm in average pore diameter, 60-90% in porosity, and 0.1-0.3 mm in thickness could be successfully fabricated using the purchased carbon fiber. The direct formic acid fuel cells using different diffusion layers for anode were fabricated and evaluated the i-V performance and crossover flux. It was found that the big pore can enhance the fuel feed rate to the anode catalyst layer under low current density (low CO2 emission), on the other hands, it did not contribute to the improvement of the fuel feed rate to the catalyst layer under higher current regions (high CO2 emissions). Small pore showed the counter trend. These results implies that the liquid feed and CO2 emissions is closely related the pore properties of diffusion layers, therefore, it is suggested that diffusion layer having suitable pore properties for direct liquid fuel cell is desired.