Direct Formic Acid Fuel Cell Research Articles

Pd nanocrystals grown on MXene and reduced graphene oxide co-constructed three-dimensional nanoarchitectures for efficient formic acid oxidation reaction

Although direct formic acid fuel cell (DFAFC) is regarded as one of the most promising energy-conversion systems, its commercialization process is impeded by the high costs of electrode catalysts as well as the sluggish catalytic reaction kinetics. Herein, we present a convenient bottom-up method to the synthesis of nanosized Pd crystals grown on 3D porous hybrid nanoarchitectures constructed from MXene (Ti3C2Tx) and reduced graphene oxide nanosheets (Pd/MX-rGO) through a co-assembly process. The as-derived 3D Pd/MX-rGO nanoarchitecture is equipped with a number of attractive textural features, such as 3D cross-linked porous networks, large specific surface area, uniform Pd dispersion, optimized electronic structure, and good electron conductivity. As a result, unusual formic acid oxidation properties in terms of high catalytic activity, strong poison tolerance, and reliable long-term stability are achieved for the 3D Pd/MX-rGO catalyst, significantly superior to those for conventional Pd catalysts supported by carbon black, graphene, and Ti3C2Tx matrixes.

Performance of Nb0.8Zr0.2 Layer-Modified AISI430 Stainless Steel as Bipolar Plates for Direct Formic Acid Fuel Cells

To improve the interfacial conductivity and corrosion resistance of AISI430 stainless steel (430SS) as bipolar plates for direct formic acid fuel cells (DFAFCs), a Nb0.8Zr0.2 layer has been successfully synthesized via the pulsed laser deposition (PLD) technique on the surface of 430SS. This Nb0.8Zr0.2 layer is smooth, uniform, and comparatively compact without any surface flaw and micropore. Investigation under the simulated anodic environment of DFAFCs (0.05 M H2SO4 + 2 ppm HF + 10 M HCOOH at 70 °C) shows that the corrosion resistance of 430SS is obviously ameliorated after the PLD modification. In addition, the interfacial contact resistance of Nb0.8Zr0.2-430SS (6.0 mΩ cm2) is much smaller than that of bare 430SS (151.3 mΩ cm2) at the clamping force of 140 N cm−2. Besides, different from the highly increased interfacial contact resistance of bare 430SS, the Nb0.8Zr0.2-430SS shows a minor increase resistance after potentiostatic tests in simulated anodic environment of DFAFCs.

Optimization of Mass Transport within Direct Formic Acid Fuel Cell Catalyst Layer via Pore Formers

Direct formic acid fuel cells (DFAFC) offer a potentially sustainable alternative to the batteries in portable devices due to their higher charge capacity, higher efficiency, and smaller size. However, due to the two-phase flow in the anode catalyst layer and the small pore size between agglomerates in the catalyst layer (~20 nm), mass transport limitations plague the performance of the DFAFC. To maximize the performance, the two-phase transport of the reactant (formic acid, liquid) and the product (carbon dioxide, gas) must be optimized. By incorporating 15 and 25 wt% MgO, the electrochemical surface area (ECSA) of the catalyst layer increased from 21.8 cm2 g-1 to 62.7 and 85.8 cm2 g-1, respectively. Furthermore, at higher potentials the porous catalyst layers improved cell performance by 86%. These improvements in ECSA and cell performance are possibly due to an enhancement of the triple-phase boundary.

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.

Corrosion inhibition of methanol towards stainless steel bipolar plate for direct formic acid fuel cell

The corrosion properties of AISI316L stainless steel (316 L SS) as bipolar plates are investigated under aqueous acid methanol solutions (0.05 M H2SO4 + 2 ppm HF + 10 M HCOOH + x M CH3OH (x = 0, 3, 6 and 9) solutions at 70 °C) to simulate the varied anodic operating conditions of direct formic acid fuel cells (DFAFCs). When the methanol content is higher, the potentiodynamic, potentiostatic polarisation and EIS tests of the 316 L SS bipolar plates all show excellent corrosion resistance. The surface morphology and the glow discharge mass spectrometer (GDMS) illustrate that the surface corrosion on 316 L SS bipolar plates is slowed down when the methanol concentration is increased. These results indicate the methanol plays the role in retarding the corrosion rate of the 316 L SS in simulated DFAFCs anodic operating conditions by restricting the proton conductivity in the test solutions. The sample tested in higher content methanol solution has smoother corroded surface and thinner passivation film, which contributes to a lower interfacial contact resistances (ICR) value.

Recent Progress of Palladium-Based Electrocatalysts for the Formic Acid Oxidation Reaction

Direct formic acid fuel cells (DFAFCs) are considered as one of the promising energy conversion devices. In recent years, Pd-based nanomaterials have attracted widespread attention for the anodic f...

CO-Reductive and O2-Oxidative Annealing Assisted Surface Restructure and Corresponding Formic Acid Oxidation Performance of PdPt and PdRuPt Nanocatalysts

Formic acid oxidation reaction (FAOR) at anode counterpart incurs at substantial high overpotential, limiting the power output efficiency of direct formic acid fuel cells (DFAFCs). Despite intense research, the lack of high-performance nanocatalysts (NCs) for FAOR remains a challenge in realizing DFAFC technologies. To surmount the overpotential losses, it is desirable to have NCs to trigger the FAOR as close to the reversible conditions (i.e. with over-potential loss as close to zero as possible). Herein, Pd-based binary and ternary NCs consisting of PdPt and PdRuPt have been synthesized via the polyol reduction method on the carbon support. As prepared PdPt and PdRuPt NCs were further subjected to heat treatment (annealed) in CO (namely PdPt-CO and PdRuPt-CO) and O2 (namely PdPt-O2 and PdRuPt-O2) atmosphere at 473 K temperature. By cross-referencing results of electron microscopy and X-ray spectroscopy together with electrochemical analysis, the effects of heat treatment under CO-reductive and O2-oxidative conditions towards FAOR were schematically elucidated. Of special relevance, the mass activity (MA) of PdPt-CO, PdPt-O2, PdRuPt-CO, and PdRuPt-O2 NCs is 1.7/2.0, 1.3/2.2, 1.1/5.5, and 0.9/4.7 Amg−1 in the anodic/cathodic scan, respectively, which is 2~4-folds improved comparative to of as-prepared PdPt (1.0/1.9 Amg−1 in anodic/cathodic scan, respectively) and PdRuPt (0.9/1.4 Amg−1 in anodic/cathodic scan, respectively) NCs. Meanwhile, after chronoamperometric (CA) stability test up to 2000 s, PdPt-CO (72 mAmg−1) and PdRuPt-CO (213 mAmg−1) NCs exhibit higher MA compared to as-prepared PdPt (54 mAmg−1) and PdRuPt (62 mAmg−1) NCs, which is attributed to the increase of surface Pt composition, especially for PdRuPt-CO NC. Besides, the stability of PdPt-O2 (15 mAmg−1) and PdRuPt-O2 (22 mAmg−1) NCs is deteriorated as compared to that of as-prepared NCs due to severe oxidation in O2 atmosphere. Of utmost importance, we developed a ternary PdRuPt catalyst with ultra-low Pt content (~2 wt.%) and significantly improved FAOR performance than pure Pt catalysts. Moreover, we demonstrated that the FAOR performance can be further enhanced by more than 30% via a unique CO annealing treatment.

Palladium-Based Nanostructures Supported on Graphene Oxide for Formic Acid Electro-Oxidation

Increments of significant Green House Gases emissions, GHG, due to persistent policies on continuing fossil fuel burning has led, in return, to more research on conversion, storage and distribution of sustainable energy sources. Direct Liquid Fuel Cells (DLFCs) coupled with Pd-based nanoparticles (PdNPs), as renewable energy sources, are capable of attaining relatively high energy conversion efficiencies, safety of operation and dependability; together, they can be applied to portable devices and transport means. For example, Direct Formic Acid Fuel Cells (DFACs) are used for these applications. This work deals with the synthesis of Pd-based electrocatalysts through a combustion method. Electrocatalysts were characterized by XRD and SEM. Further, the ensuing electrochemical characterization was carried out by means of the electrocatalysts activation, CO adsorption/oxidation and formic acid electro-oxidation. Figure 1

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.

TiO2 Nanotubes with Pt and Pd Nanoparticles as Catalysts for Electro-Oxidation of Formic Acid.

In the present work, the magnetron sputtering technique was used to prepare new catalysts of formic acid electrooxidation based on TiO2 nanotubes decorated with Pt (platinum), Pd (palladium) or Pd + Pt nanoparticles. TiO2 nanotubes (TiO2 NTs) with strictly defined geometry were produced by anodization of Ti foil and Ti mesh in a mixture of glycerol and water with ammonium fluoride electrolyte. The above mentioned catalytically active metal nanoparticles (NPs) were located mainly on the top of the TiO2 NTs, forming ‘rings’ and agglomerates. A part of metal nanoparticles decorated also TiO2 NTs walls, thus providing sufficient electronic conductivity for electron transportation between the metal nanoparticle rings and Ti current collector. The electrocatalytic activity of the TiO2 NTs/Ti foil, decorated by Pt, Pd and/or Pd + Pt NPs was investigated by cyclic voltammetry (CV) and new Pd/TiO2 NTs/Ti mesh catalyst was additionally tested in a direct formic acid fuel cell (DFAFC). The results so obtained were compared with commercial catalyst—Pd/Vulcan. CV tests have shown for carbon supported catalysts, that the activity of TiO2 NTs decorated with Pd was considerably higher than that one decorated with Pt. Moreover, for TiO2 NTs supported Pd catalyst specific activity (per mg of metal) was higher than that for well dispersed carbon supported commercial catalyst. The tests at DFAFC have revealed also that the maximum of specific power for 0.2 Pd/TiO2 catalyst was 70% higher than that of the commercial one, Pd/Vulcan. Morphological features, and/or peculiarities, as well as surface composition of the resulting catalysts have been studied by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and chemical surface analytical methods (X-ray photoelectron spectroscopy—XPS; Auger electron spectroscopy—AES).

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.

Improving the electrocatalytic activity for formic acid oxidation of bimetallic Ir–Zn nanoparticles decorated on graphene nanoplatelets

A graphene nanoplatelet (GNP)-supported Ir–Zn catalyst (Ir–Zn/GNP) was fabricated by H2 reduction to discover an alternative for non-platinum and non-palladium catalysts as an anode catalyst in direct formic acid fuel cell (DFAFC). The obtained Ir–Zn/GNP catalyst with ratio of Ir:Zn = 50:50 (Ir50Zn50/GNP) exhibited better electrocatalytic activity than GNP-supported iridium catalyst (Ir/GNP) for formic acid oxidation. Although the oxidation peak current density of Ir50Zn50/GNP was slightly lower than that of Ir/GNP, the oxidation peak potential shifted more negatively (193 mV) than Ir/GNP with higher value of the ratio of forward scan to reverse the scan peak current (If/Ib). The presence of Zn also enhanced the power density and current generation with increased performance stability in a passive DFAFC cell tests. The improvement of the electrochemical performance was ascribed to the ensemble effect where the addition of Zn could modify the Ir atom arrangement, thereby promoting the oxidation through dehydrogenation pathway. However, extremely high Zn content would inhibit oxidation capability because Zn atoms might reduce the Ir catalytic sites. A new alternative for non-Pt and non-Pd anode catalysts for DFAFC applications was successfully achieved.

Zirconia Modified Pd Electrocatalysts for DFAFCs

In order to enhance the Pd based anodic catalysts for direct formic acid fuel cells (DFAFCs), the research work includes increasing catalyst activity and preventing CO poison. In this study, various zirconium oxides-modified multi-walled carbon nanotubes (MWCNTs) were prepared as the supports of Pd catalysts for DFAFCs by adjusting the preparation parameters: metal adding, sintering temperature and atmospheres. The prepared pure zirconia has both monoclinic and tetragonal phases. The addition of MWCNTs depresses the growth of monoclinic phase. A small amount of Pd adding allows both monoclinic and tetragonal zirconia structures to appear again. Pd nanoparticles of 20 wt% synthesized on MWCNTs and tetragonal ZrO2/MWCNTs have similar particle size, while Pd/[Pd:ZrO2/AO-MWCNTs-300Air-900Ar] have more nanoparticles aggregation. The electrochemical surface area can be improved by adding zirconia which implies those zirconia modified Pd catalysts better electrocatalytic performance. By analyzing the maximum current density and the corresponding potential, Pd/AO-MWCNTs are inferred to undergo the formic acid direct oxidation initially. The Pd catalysts modified by tetragonal ZrO2 have higher current density. Those having both tetragonal and monoclinic ZrO2 modified Pd catalysts have lower potential of formic acid oxidation. All the Pd based catalysts with zirconia modification possess better CO resist ability and electrocatalytic activity. Pd/[ZrO2/AO-MWCNTs-300Air-900Ar] and Pd/[Pd:ZrO2/AO-MWCNTs-300Air-900Ar] which catalyze formic acid in direct oxidation path are the two best catalysts.

A Review of Pd Based Multimetallic Anode Electrocatalysts for Direct Formic Acid Fuel Cells

A Review of Pd Based Multimetallic Anode Electrocatalysts for Direct Formic Acid Fuel Cells

In Situ Exfoliation and Pt Deposition of Antimonene for Formic Acid Oxidation via a Predominant Dehydrogenation Pathway.

Direct formic acid fuel cell (DFAFC) has been considered as a promising energy conversion device for stationary and mobile applications. Advanced platinum (Pt) electrocatalysts for formic acid oxidation reaction (FAOR) are critical for DFAFC. However, the oxidation of formic acid on Pt catalysts often occurs via a dual pathway mechanism, which hinders the catalytic activity owing to the CO poisoning. Herein, we directly exfoliate bulk antimony to 2D antimonene (Sb) and in situ load Pt nanoparticles onto antimonene sheets with the assistance of ethylenediamine. According to the Bader charge analysis, the charge transfer from antimonene to Pt occurs, confirming the electronic interaction between Pt and Sb. Interestingly, antimonene, as a cocatalyst, alters the oxidation pathway for FAOR over Pt catalyst and makes FAOR follow the more efficient dehydrogenation pathway. The density functional theory (DFT) calculation demonstrates that antimonene can activate Pt to be a lower oxidative state and facilitate the oxidation of HCOOH into CO2 via a direct pathway, resulting in a weakened intermediate binding strength and better CO tolerance for FAOR. The specific activity of FAOR on Pt/Sb is 4.5 times, and the mass activity is 2.6 times higher than the conventional Pt/C.

MEMS-Based Microfluidic Fuel Cell for In Situ Analysis of the Cell Performance on The Electrode Surface

The present study investigates various effects of MEMS-based microfluidic fuel cell on the performance of direct formic acid microfluidic fuel cells that breathe air as an oxidant. A miniaturized fuel cell of the structure and design of a typical T-shaped air- breathing Direct Formic Acid Fuel Cell with micro channel is 1.5 mm x 25 mm in width multiply length. Both anode and cathode electrode having a width and length of 0.6 mm and 20 mm, respectively, with an electrode spacing of 0.3 mm. An air-breathing microfluidic fuel cell having a 0.6 mm in width and 20 mm in length that is placed on cathode GDE down-side. In such systems for the fluid delivery, both formic acid (0.5 M) as a fuel solution mixing sulfuric acid (0.5 M) at a node channel side and as an electrolyte used sulfuric acid (0.5 M) place take on the cathode channel side are injected together into the end of the channel outlet by two syringe pumps. Firstly, a three-dimensional microfluidic fuel cell model was established using Computational Fluids Dynamics to simulate the fuel cell performance. Further, both V-I curves obtained from simulation and published experimental data under similar operating condition were compared to assure the validity of the simulation. Modelling the transport and electrochemical phenomena were described with hydrodynamic equations, the porous media flow, mass transport, electrochemical reaction and charge equation. The porous media flow in the gas diffusion layer was described by Brinkman equation. The Butler-Volmer equations were applied to get the V-I-P curves. An anode electrode surface performance, respectively, is presented.

Effective carbon nanotube supported metal (M=Au, Ag, Co, Mn, Ni, V, Zn) core Pd shell bimetallic anode catalysts for formic acid fuel cells

At present, CNT supported Pd and core-shell Pd-based catalysts are synthesized by employing the NaBH4 reduction method to investigate on formic acid electrooxidation (FAEO) activity. These catalysts are characterized by XRD, TEM, HRTEM, and XPS. The XRD results display that the electronic state of catalysts changed by second metal addition to Pd. TEM results reveal that Au and Pd are homogeneously distributed. XPS results of AucorePdshell/CNT catalyst show that Au and Pd atoms used in the preparation of the catalyst are obtained mainly in elemental state. The FAEO activity, stability, and resistance of these catalysts are investigated by employing cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The CV results show that AucorePdshell/CNT catalyst having 16.42 mAcm−2 specific activity and 4978.23 mA mg−1 Pd mass activity is better than other catalysts. In addition, the AucorePdshell/CNT (21 m2/g) catalyst has better electrochemical active surface area (ECSA) value as 5.25 times compared with Pd/CNT catalyst. Direct formic acid fuel cell (DFAFC) performances are performed at different temperatures for AucorePdshell/CNT and NicorePdshell/CNT catalysts. The specific activity of AucorePdshell/CNT catalyst is 2.5 times higher than the value for NicorePdshell/CNT catalyst. AucorePdshell/CNT catalyst is a promising catalyst for DFAFCs.

Formic acid decomposition-inhibited intermetallic Pd3Sn2 nanonetworks for efficient formic acid electrooxidation

Inhibiting formic acid decomposition on Pd-based electrocatalysts is a major challenge for realizing the commercialization of direct formic acid fuel cells (DFAFCs). Inspired by the catalytic characteristics of formic acid decomposition/electrooxidation on Pd-based materials, here we synthesize intermetallic bimetallic Pd–Sn nanonetworks (NNWs) to deal with this problem. Compared to commercial Pd black with high catalytic activity, the strong Pd–Sn electronic interaction in intermetallic Pd3Sn2 NNWs induces the complete inhibition of formic acid decomposition at 80 °C. Parallelly, Pd3Sn2 NNWs exhibit mass activity of 448 A gPd−1 for formic acid electrooxidation due to Pd–Sn synergistic effect, which is 2.1 times higher than that of commercial Pd black. The stable intermetallic structure and three-dimensionally interconnected architecture endow Pd3Sn2 NNWs with better electrochemical and electrocatalytic durability, suggesting promising cost-effective anode catalysts for DFAFCs.

The Mixture of Nanoparticles of RuO2 and Pt Supported on Ti as an Efficient Catalyst for Direct Formic Acid Fuel Cell

An active coating, composed of a mixture of nanocrystals of RuO2 with the rutile structure and nanocrystals of metal Pt, was thermally synthetized on a titanium substrate. Cyclic voltammograms and polarization curves showed that the catalytic activity of the coating for the formic acid oxidation in an acidic solution increased with an increase in the RuO2 content, reaching the maximum value at 50 mol % RuO2. Additionally, further increase in the RuO2 content resulted in a decline of the catalytic activity. The catalytic effect was attributed to a bifunctional mechanism and an electronic effect. The bifunctional mechanism had a dominant role and was based on the fact that Ru–OH species were formed on Ru atoms of RuO2 at more negative potentials than on Pt. Those species oxidized the adsorbed COad and HCOOad—species on adjacent Pt atoms of clusters of metal Pt and thus discharge them to oxidize new HCOOH molecules.