Direct Formic Acid Fuel Cell Performance Research Articles

Effect of Synchrotron X-ray Irradiation Time on the Particle Size and DFAFC Performance of Pd/CNT Catalysts.

Global energy sources are limited, and energy requirements are ever-increasing due to the demand for developments in human life and technology. The environmentally friendly direct formic acid fuel cell (DFAFC) is an attractive electronic device due to its clean energy. In a DFAFC, an anodic catalyst plays an important role concerning the oxidation pathway and activity. In the present study, palladium (Pd) was synthesized by synchrotron X-ray photoreduction using various irradiation times (0.5-4 min) to control the particle size. An acid-treated carbon nanotube (A-CNT) was used as the template for Pd deposition. The A-CNT and Pd/A-CNT were examined using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy to reveal the microstructural characteristics. Electrochemical evaluation, electrocatalytic activity, and the DFAFC performance of so-obtained Pd/A-CNT catalysts were investigated. The experiment's results showed that the Pd/A-CNT-2 (i.e., synchrotron photoreduction for 2 min) underwent a direct formic acid oxidation pathway and possessed a high ECSA value of 62.59 m2/gPd and superior electrocatalytic activity of 417.7 mA/mgPd. In a single DFAFC examination, the anodic Pd/A-CNT-2 catalyst had a power density of 106.2 mW/mgPd and a relatively long lifetime of 2.91 h. Pd/A-CNT-2 anodic catalysts synthesized by surfactant-free synchrotron X-ray photoreduction with a rapid processing time (2 min) are potential candidates for DFAFC applications.

(Digital Presentation) Power-Generation and Mass-Transport Characteristics of Direct Formic Acid Fuel Cell Using Pore-Designed Anode Electrode

Controlling of mass transport in the anode catalyst layer has become one of the major challenges in Direct Formic Acid Fuel Cells (DFAFCs) owing to the poor formic acid transport and crossover. This study is aim to introduce the microfiber-pores designed anode catalyst layers by mean to improve the mass transport limitation and eventually improving the performance of DFAFCs. Polystyrene fibers (PSFs) were fabricated with different diameter by electrospinning prior to control their length by ultrasonic homogenization. Different amount of PSF as a pore forming agent were then added to the catalyst ink before catalyst coated membrane (CCM) were made by spraying the catalyst ink on the membrane. The CCM were then soaked in ethyl acetate solution to remove the PSF in order to improve the porous structure of anode catalyst layer. Different diameter and amount of PSFs exhibited different pore properties of the catalyst layer and its effect on the mass transport and the performance of DFAFC were then investigated. From the results, the microfiber-pores designed anode catalyst layers showed better performance remarkably at the higher current density region as compared to the conventional anode catalyst layer. Moreover, it was also found that there were optimum diameter and amount of PSF used for the highest performance of DFAFC. This could be attributed to the existence of the microfiber-pores have provide larger active catalyst region which accelerate the fuel transport and the CO2 emission in anode catalyst layer. Thus, these results indicate that the introduction of the microfiber-pores on the anode catalyst layer is a promising approach in order to improve the mass transport resistance, leading to enhance the DFAFCs performance.

A Competent MWCNT-Grafted MnOx/Pt Nanoanode for the Direct Formic Acid Fuel Cells

A novel “MnOx/Pt/MWCNT-GC” nanocatalyst is recommended for the electrooxidation of formic acid (EOFA), the principal anodic reaction in the direct formic acid fuel cells (DFAFCs). The sequential (layer-by-layer) protocol was employed to prepare the catalyst through the electrodeposition of Pt (nano-Pt) and manganese oxide (nano-MnOx) nanoparticles onto the surface of a glassy carbon (GC) electrode supported with multiwalled carbon nanotubes (MWCNTs). The nano-MnOx could successfully mediate the mechanism of EOFA by accelerating the charge transfer, “electronic effect”. On the other hand, MWCNTs could enhance the catalytic performance by changing the surface geometry that inhibited the adsorption of poisoning CO, which is a typical intermediate in the reaction mechanism of EOFA that is responsible for the potential deterioration of the catalytic performance of DFAFCs. Interestingly with this modification, a significant enhancement in the catalytic activity and stability toward EOFA was achieved. Several techniques will be employed to evaluate the catalyst’s morphology, composition, crystal structure, and activity and further to understand the role of each of the nano-MnOx and MWCNTs in the catalytic enhancement.

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.

Improving the electrocatalytic performance of Pd for formic acid electrooxidation by introducing tourmaline

Palladium is the most effective catalyst with high initial activity for formic acid electrooxidation (FAEO) in direct formic acid fuel cells (DFAFCs), but the low performance of DFAFC comparing to H2-PEMFC and the accumulation of COad poisoning species on palladium restrict the commercialization of DFAFC. Herein, a novel and efficient FAEO catalyst, tourmaline modified Pd (Pd/TNP@SC) are prepared. A class of core@shell structured carbon coated tourmaline (TNP@SC) are equipped as the catalyst support to efficiently utilize the spontaneous polarization-induced electric field and far-infrared radiation of tourmaline for FAEO reaction. Physical and electrochemical measurements suggest that the existence of electric field and far-infrared radiation of tourmaline promote synthesizing smaller Pd nanoparticles, weakening the Pd-O bond, increasing molecular vibration and migration rate, and dissociating water molecules into OHad to spontaneously convert COad into CO2. Even under potentials applied higher than 0.3 V (vs. Ag/AgCl), Pd/TNP@SC catalysts still have high FAEO activity. Among all the Pd/TNP@SC catalysts investigated in this study, Pd/TNP@SC-800 owns the strongest electric field and far-infrared radiation, exhibits the best activity for FAEO, which is 3.1 times higher than that of tourmaline-free catalyst (Pd/SC)), and excellent CO-tolerance during FAEO reaction. This work provides an effective catalyst design strategy for FAEO.

Substantially Enhanced Power Output and Durability of Direct Formic Acid Fuel Cells at Elevated Temperatures

AbstractDevelopment of direct formic acid fuel cell (DFAFC) is significantly constrained by low output performance and poor durability because of the sluggish formic acid oxidation reaction (FAOR) and the poisoning by COads intermediate on the Pt‐based electrocatalyst at low operating temperatures. By operating DFAFCs at elevated temperatures, the peak power density (PPD) of the cell based on the Pt/C catalyst increases significantly. For example, the PPD of DFAFC reaches 198 mW cm−2 at 240 °C, eight times higher than that of the DFAFC at 70 °C. The study shows the surprising transition in power performance of DFAFCs at elevated temperatures. The increase of PPD for DFAFC against temperature is 121 mW cm−2/100 °C at temperatures above 115 °C, almost three times higher than the 45 mW cm−2/100 °C obtained at lower temperatures. The fundamental reason for the substantially enhanced power output and durability is the gradual transformation of the reaction kinetics from sluggish direct FAOR at low temperatures to fast H2 oxidation reaction at elevated temperatures due to the increased in situ decomposition of formic acid on Pt/C catalysts at temperatures above 100 °C. This study demonstrates that operation at temperatures above 160 °C is most effective to promote performance and durability of DFAFCs.

Influence of the Diffusion Media Structure for the Bubble Distribution in Direct Formic Acid Fuel Cells

Direct formic acid fuel cells (DFAFCs) have received considerable attention because they can generate a higher power density compared to other direct liquid fuel cells. However, when generated CO2 bubbles are retained in the anode’s porous transport layer (PTL), the performance of the DFAFCs deteriorates. The gas–liquid two-phase flow behavior within a PTL is not clear; therefore, in this work the power-generation characteristics of DFAFCs using two types of PTL, carbon paper and carbon cloth, were investigated. It was found that the maximum current density was approximately 60 mA cm−2 higher with the carbon cloth than with the carbon paper. The CO2 bubble distribution in the anode’s PTLs was visualized by X-ray computed tomography and discuss the effects of the bubbles on the power-generation performance of DFAFCs. We found that interstices in a carbon-cloth PTL provided pathways for bubble migration and release to the channel, so that the bubbles did not deteriorate the power output. Bubble accumulation in a carbon-paper PTL led to a drop in power output, confirming that the structure of the PTL and the CO2 bubbles affect the power-generation characteristics.

Carbon supported palladium-copper bimetallic catalysts for promoting electrochemical oxidation of formic acid and its utilization in direct formic acid fuel cells

Carbon supported palladium-copper (Pd-Cu) bimetallic catalysts (PdxCuy/Cs) are fabricated by modified polyol method to enhance the reaction rate of formic acid oxidation reaction (FAOR) and the performance of direct formic acid fuel cell (DFAFC) through weakening the bond with the intermediate of formic acid. According to the evaluations, when the ratio of Pd and Cu is 3 : 1 (Pd3Cu1/C), catalytic activity is best. Its maximum current density is 1.68-times better than that of commercial Pd/C. Even from the optical and spectroscopic characterizations, such as TEM, EDS, XPS and XRD, Pd3Cu1/C shows an optimal particle size and a higher degree of alloying. This is because in Pd3Cu1/C catalyst, the d-band center that induces the weakening in adsorption of formate anion groups to Pd surface is most positively shifted, and this positive shift promotes the reaction rate of FAOR, which is the rate determining step. When the performance of DFAFCs using the PdxCuy/C catalysts is measured, the maximum power density (MPD) of DFAFC using Pd3Cu1/C catalyst is 158 mW cm−2, and this is the best MPD compared to that of DFAFCs using other PdxCuy/C catalysts. In addition, in a comparison with commercial Pd/C catalyst, when the same amount of catalyst is loaded, MPD of DFAFC using Pd3Cu1/C catalyst is 22.5% higher than that of DFAFC using commercial Pd/C.

The Effect of CO2 Bubble Distribution on Power Generation Performance of a Direct Formic Acid Fuel Cell

Introduction Recently, formic acid is expected as one of the energy career for renewable energy. Especially, direct formic acid fuel cells (DFAFCs) which use formic acid as fuel, have received considerable attention since they can generate higher power density than the other direct liquid fuel cells [1]. However, CO2 gas is generated in the anode reaction when DFAFCs are operating. If CO2 bubbles stay in the anode gas diffusion layer (GDL) the mass transport resistance in GDL increases and the power generation performance of DFAFCs decreases with the lapse of time. In this study, we have investigated the effect of CO2 bubble distribution on power generation performance by visualizing the CO2 bubble distribution in DFAFCs during power generation using X-ray CT. Experimental A single cell with 1 cm2 of active area was used. We used NR-212 as proton exchange membrane, PEM. Pd/C was used for anode catalyst and Pt/C was used for cathode catalyst. Moreover, two types of GDL with different structures of carbon paper and carbon cloth were used. The voltage sweep was performed at a sweep rate of -5 mV / sec until the cell voltage turned from the open circuit voltage to 0 V, and the cell voltage and current density during the sweep were recorded. A three-dimensional measurement X-ray CT apparatus (TDM-1000H-Ⅱ (2K), Yamato Scientific) was used for visualizing CO2 bubble distribution in DFAFCs. It took 15 minutes to visualize and the spatial resolution was 2.7 μm. Results and discussion From the measurement of the power generation characteristics, it was found that the maximum current density is higher with carbon cloth GDL than with carbon paper GDL, despite the lower open circuit voltage. In addition, using carbon paper GDL, the gradient of polarization curve became steep in the high current density region. These phenomena are generally considered to be caused by mass transport, and in this experiment it is thought that this is probably due to the effect of bubbles in the anode GDL. Therefore, in order to investigate the influence of bubbles in the anode GDL, visualization was performed. Fig. 1 shows the CO2 bubble distribution in the anode GDL at high current density operation using each GDL. These figures are three-dimensional representation of the bubble distribution in the anode GDL averaged over 15 minutes of visualization time. Furthermore, these are top views seen from the vertically upward direction of the GDL plane, the white part indicates that bubbles exist. As shown in Fig. 1, using carbon paper GDL, bubbles were present under most of the rib and also present under the channel, which was thought to cause the power generation performance degradation due to the mass transport. On the other hand, with the carbon cloth GDL, there were almost no bubbles under the channel, and bubbles and voids were concentrated under the rib. It is considered that in the carbon cloth, the bubbles were concentrated in part and the discharge path of the bubbles was formed, so that the bubbles were efficiently discharged and the power generation performance did not decrease even in the high current density region. Reference 1) Y. Zhu, Z. Khan, R.I. Masel, Journal of Power Sources, 139, 15-20 (2005) Figure 1

Synthesis and characterization of Co, Zn, Mn, V modified Pd formic acid fuel cell anode catalysts

In this study, carbon nanotube (CNT) supported Pd50Co50, Pd50V50, Pd50Mn50, and Pd50Zn50 bimetallic catalysts are prepared by using sodium borohydride (NaBH4) reduction method to investigate their formic acid electrooxidation (FAEO) activities. These catalysts are characterized by using X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES), and X-ray Photoelectron Spectroscopy (XPS). The XRD results show that the electronic state of catalysts varied by second metal addition to Pd. TEM results reveal that Pd and Co are homogeneously distributed. The result of Pd43Co57/CNT obtained by ICP-OES analysis of Pd50Co50/CNT catalyst shows that the synthesis was successfully synthesized. XPS results of Pd50Co50/CNT and Pd50Zn50/CNT catalysts showed that Pd, Zn, and Co atoms used in the preparation of the catalysts were obtained mainly in their elemental state. In addition, FAEO activity and stability of these catalysts are examined by using cyclic voltammetry (CV) and chronoamperometry (CA). Pd50Co50/CNT indicated the highest specific and mass activities with 6.89 mA/cm2 and 649.69 mA/mg Pd, respectively. Direct formic acid fuel cell (DFAFC) performances are performed in different temperatures for Pd50Co50/CNT catalyst. The specific current for DFAFC performance of this catalyst was evaluated as 5.71, 6.87, and 2.43 mA/cm2 at 18 °C, 30 °C, and 60 °C cell temperature at 0.5 V, respectively.

The Effect of CO2 Bubble Distribution on Power Generation Performance of a Direct Formic Acid Fuel Cell

Direct formic acid fuel cells (DFAFCs) have received considerable attention because they can generate higher power density compared with other direct liquid fuel cells. However, when the generated CO2 bubbles are retained in the anode porous transport layer (PTL), the performance of DFAFCs deteriorates. In this study, power generation characteristics of DFAFCs using two types of PTL, viz. carbon paper and carbon cloth, were investigated. It was found that the maximum current density is about 60 mA/cm2 higher with the carbon cloth than with the carbon paper. The CO2 bubble distributions in anode PTLs were visualized during the operation using X-ray computed tomography, and the visualized images showed that the PTL structure affected the CO2 bubble distribution, and that the transport paths of formic acid through liquid phase are tortured. Thus, it could be concluded that the transport characteristics of CO2 bubbles affect the power generation characteristics of DFAFCs.

Three-dimensional CFD modeling of a direct formic acid fuel cell

A three-dimensional (3D) with one straight channel computational fluid dynamics (CFD) model is developed by using the ESI-CFD software to investigate the effect of varying operating parameters on the performance of direct formic acid fuel cell (DFAFC) and formic acid crossover from the anode to the cathode side through the membrane. Formic acid concentration (4 M–10 M), temperature (313 K–353 K), anode stoichiometry (1.5–3.0), and cathode stoichiometry (2.0–3.0) are the selected operating parameters in this study. Validation results of the DFAFC are in reasonable agreement with the typical trends reported in the literature on DFAFC performance. Simulation results indicate that formic acid concentration, temperature, anode, and cathode stoichiometry influenced the DFAFC performance and the formic acid crossover. The increments of formic acid concentration or stoichiometric ratio will improve the cell performance; however, the current densities obtained are declining to the increasing temperature. The increase in temperature of the formic acid concentration is found to lead to the decrease in performance. For the formic acid crossover phenomenon, the formic acid crossover flux increases with the increments of formic acid concentration, DFAFC operating temperature, and anode and cathode stoichiometric ratios.

Superior electrocatalysis of formic acid electro-oxidation on a platinum, gold and manganese oxide nanoparticle-based ternary catalyst

A novel “MnOx/Au/Pt” ternary nanocatalyst is recommended for formic acid electro-oxidation (FAO), the principal anodic reaction in direct formic acid fuel cells (DFAFCs). The protocol employed to prepare the catalyst utilized the sequential (layer-by-layer) electrodeposition of Pt (nano-Pt), Au (nano-Au) and manganese oxide (nano-MnOx) nanoparticles onto the surface of a glassy carbon (GC) support. The nano-Au enhanced the catalytic performance by changing the surface geometry to inhibit the adsorption of poisoning CO, which is a typical intermediate in the reaction mechanism of FAO, producing a potential deterioration of the catalytic performance of DFAFCs. On the other hand, nano-MnOx could successfully mediate the mechanism of FAO by accelerating the charge transfer and imparting an enhanced catalytic stability during long continuous operation. Interestingly, with this modification of the Pt/GC electrode by nano-Au and nano-MnOx, a significant (ca. 67 times that obtained at the Pt/GC electrode) enhancement in the catalytic activity toward FAO was achieved.

Pd[sbnd]Bi bimetallic catalysts including polyvinylpyrrolidone surfactant inducing excellent formic acid oxidation reaction and direct formic acid fuel cell performance

PdBi bimetallic catalysts are synthesized while their catalytic activity and stability for formic acid oxidation reaction (FAOR) and direct formic acid fuel cell (DFAFC) performance are evaluated. According to investigations, Pd2Bi1/C catalyst including low Pd amount promotes oxygen desorption with enhancement in CO poisoning resistance. With that, indirect formic acid oxidation reaction (IFAOR) and its stability are improved. To further improve the FAOR, polyvinylpyrrolidone (PVP) surfactant is contained due to its amphiphilic property reducing Bi aggregation. To determine optimal amount of the PVP, analysis using TEM and XPS is performed and the results are verified by density functional theory (DFT). According to TEM, in 0.22 PVP-Pd2Bi1/C catalyst, PdBi has small size (∼5 nm) and is well-dispersed with widest Ed- EF of 3.85 eV, proving the catalyst induces effective CO-poisoning resistance and less Bi aggregation. These results are also compatible with trend in FAOR measured by cyclic voltammogram (CV). Even long-term stability, the catalyst maintains catalytic activity well. The best performance of DFAFC using the catalyst (32.7 mW cm−2·Pdg−1) indicates that 0.22 PVP- Pd2Bi1/C is excellent catalyst for FAOR and DFAFC performances.

Towards improving the catalytic activity and stability of platinum-based anodes in direct formic acid fuel cells

The current investigation presents a novel catalyst for formic acid electro-oxidation (FAO); the essential anodic reaction in direct formic acid fuel cells (DFAFCs). The catalyst is developed by a sequential electrodeposition method for Pt (PtNPs), Au (AuNPs) and nickel oxide (nano-NiOx) nanoparticles onto the surface of a glassy carbon (GC) electrode. The objective of this modification was solely dedicated to the improvement of the electrode's catalytic activity by overcoming the CO poisoning, which is usually responsible for the deterioration of the catalytic performance of DFAFCs. The deposition sequence of the catalyst ingredients (PtNPs, AuNPs, and nano-NiOx) was adjusted to optimize the electrocatalytic activity and stability of the catalyst towards FAO. Interestingly, the highest catalytic activity and stability towards FAO was obtained at the NiOx/Au/Pt/GC electrode in which PtNPs were directly deposited onto the GC electrode followed by AuNPs then nano-NiOx. The discussion is oriented to adopt the role of the ternary catalyst ingredients in the catalytic enhancement.

A parametric study of the direct formic acid fuel cell (DFAFC) performance and fuel crossover

The effect of formic acid concentration (2–20 M), operating temperature (30–70 °C), and relative humidity (RH 40–90%) on the direct formic acid fuel cell (DFAFC) performance and fuel crossover were studied. In addition, air and oxygen were used to investigate the effect of oxidant flow rate on DFAFC performance and fuel crossover by operating the DFAFC under three modes of reactant supply: passive, semi passive (oxidant supplied), and active (both oxidant and fuel supplied). Fuel crossover was determined by measuring the percentage of exhausted carbon dioxide (CO2) at the cathode using a CO2 analyzer, from which the equivalent formic acid crossover flux was calculated. The results indicate that the DFAFC performance and fuel crossover were affected by formic acid concentration, temperature, humidity, oxidant flow rate, and the mode of operation. Optimums of these operating parameters were established for obtaining high performance of the DFAFC. The relationships between these parameters and the performance and fuel crossover of the DFAFC are discussed in this paper.

Effect of Different Types of Microporous Layer Toward the Performance of Direct Formic Acid Fuel Cell

Typical electrodes of anode and cathode are supported on macroporous backing layer with additional microporous carbon layer. The effect of the gas diffusion layer (GDL) on the cell performance in a direct formic acid fuel cell (DFAFC) has been characterized. The performance of DFAFC might be hindered by mass transfer limitation due to hydrophilicity properties of the formic acid. By measuring the contact angle and SEM photograph, the physicochemical and surface morphology of different types of GDL can be classified. Meanwhile, the effects of carbon materials such as carbon black, carbon nanofibre and carbon nanotube as a microporous layer on the backing layer of carbon paper were investigated on the basis of the characterization and the performance. From the results, it was obtained that CNF was a good material as microporous layer due to the properties of in plane conductivity, high current in cyclic voltammetry and also had smoother surface on the morphology test.

Performance Enhancement by Adaptation of Long Term Chronoamperometry in Direct Formic Acid Fuel Cell using Palladium Anode Catalyst

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 performance, palladium (Pd) and platinum (Pt) are used as anode and cathode catalysts, respectively, and are applied to a Nafion 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 . By characterizations like TEM, Z-potential, CV and electrochemical impedance spectroscopy, it is evaluated that such dissolved 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.

Effect of deactivation and reactivation of palladium anode catalyst on performance of direct formic acid fuel cell (DFAFC)

In the present study, degradation and recovery in cell performance of direct formic acid fuel cells (DFAFCs) are investigated. For DFAFC tests, palladium (Pd) and platinum (Pt) are used as anode and cathode catalysts, respectively, and are applied to a Nafion membrane by catalyst-coated membrane (CCM) spraying. As multiple repeated DFAFC operations are performed, the cell performance of DFAFC is steadily degraded. This behavior is ascribed to the electrooxidation of Pd into Pd–OH, which occurs between 0.1 and 0.55 V. To investigate the dependency of the cell performance on the Pd–OH and to evaluate how the cell performance is regenerated, cyclic voltammetry (CV) tests are executed. In CV experiments where the voltages applied to the DFAFC single cell are lower than 0.7 V vs. DHE, the cell performance is further deactivated due to continuous production of Pd–OH. Conversely, in CV experiments where the voltage is higher than 0.9 V vs. DHE, cell performance is reactivated due to redox reactions of Pd–OH into Pd–O and Pd–O into Pd. ATR-FTIR and XPS are used to confirm the transformations of Pd.

Origin of performance degradation of palladium-based direct formic acid fuel cells

The very limited durability of Pd-based anode for direct formic acid fuel cells (DFAFCs) has seriously restricted their practical application. However, the mechanistic clarification on how to remove the poisoning species and to reactivate the Pd-based anode still remains a big challenge. In this work, we have found that Pd oxides/hydrous oxides (POHOs) play a crucial role in promoting better performance and minimizing performance degradation of the Pd-based DFAFCs. The POHOs are unstable under DFAFC conditions. The intrinsic presence or introduction of Pd oxides/hydrous oxides during electrocatalysis of formic acid oxidation is found to promote elimination of poisoning species, thereby leading to a better performance of DFAFCs. The consumption of Pd oxides/hydrous oxides under DFAFC conditions leads to formation of adsorbed CO-like intermediates that are non-removable, and contribute to the irreversible performance degradation. The present study provides new insights into the degradation mechanism of Pd-based DFAFCs and suggests design features for new durable Pd-based nanostructured catalysts.