Formic Acid Fuel Cells Research Articles

Evaluation of Pd Nanoparticle-Decorated CeO2-MWCNT Nanocomposite as an Electrocatalyst for Formic Acid Fuel Cells

In this work, CeO2-modified Pd/CeO2-carbon nanotube (CNT) electrocatalyst for the electro-oxidation of formic acid has been investigated. The support CNT was first modified with different amounts (5–30 wt.%) of CeO2 using a precipitation-deposition method. The electrocatalysts were developed by dispersing Pd on the CeO2-CNT supports using the borohydride reduction method. The synthesized electrocatalysts were analyzed for composition, morphology and electronic structure using x-ray diffraction (XRD), scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) techniques. The formation of Pd nanoparticles on the CeO2-CNT support was confirmed using TEM. The activity of Pd/CeO2-CNT and of Pd-CNT samples upon oxidation of formic acid was evaluated by using carbon monoxide stripping voltammetry, cyclic voltammetry, and chronoamperometry. The addition of moderate amounts of cerium oxide (up to 10 wt.%) significantly improved the activity of Pd/CeO2-CNT compared to the unmodified Pd-CNT. Pd/10 wt.% CeO2-CNT showed a current density of 2 A mg−1, which is ten times higher than that of the unmodified Pd-CNT (0.2 A mg−1). Similarly, the power density obtained for Pd/10 wt.% CeO2-CNT in an air-breathing formic acid fuel cell was 6.8 mW/cm2 which is two times higher than Pd-CNT (3.2 mW/cm2), thus exhibiting the promotional effects of CeO2 to Pd/CeO2-CNT. A plausible justification for the improved catalytic performance and stability is provided in the light of the physical characterization results.

Efficient Direct Formic Acid Fuel Cells (DFAFCs) Anode Derived from Seafood waste: Migration Mechanism

Commercial Pt/C anodes of direct formic acid fuel cells (DFAFCs) get rapidly poisoned by in-situ generated CO intermediates from formic acid non-faradaic dissociation. We succeeded in increasing the Pt nanoparticles (PtNPs) stability and activity for formic acid oxidation (DFAFCs anodic reaction) by embedding them inside a chitosan matrix obtained from seafood wastes. Atop the commercial Pt/C, formic acid (FA) is predominantly oxidized via the undesired poisoning dehydration pathway (14 times higher than the desired dehydrogenation route), wherein FA is non-faradaically dissociated to CO resulting in deactivation of the majority of the Pt active-surface sites. Surprisingly, PtNPs chemical insertion inside a chitosan matrix enhanced their efficiency for FA oxidation significantly, as demonstrated by their 27 times higher stability along with ~400 mV negative shift of the FA oxidation onset potential together with 270 times higher CO poisoning-tolerance compared to that of the commercial Pt/C. These substantial performance enhancements are believed to originate from the interaction of chitosan functionalities (e.g., NH2 and OH) with both PtNPs and FA molecules improving FA adsorption and preventing the PtNPs aggregation, besides providing the required oxygen helping with the oxidative removal of the adsorbed poisoning CO-like species at low potentials. Additionally, chitosan induced the retrieval of the Pt surface-active sites by capturing the in-situ formed poisoning CO intermediates via a so-called “migration mechanism”.

Improved Anode Catalyst for Formic Acid Fuel Cells

The use of direct formic acid fuel cells (DFAFCs) in portable electronic devices can improve available power density and convenience, compared to today’s rechargeable batteries. Unfortunately, current DFAFC anode catalysts either have high parasitic overpotentials and/or deactivate over time. This deactivation causes a decrease in sustained performance of the catalyst over time.[1] A typical anode catalyst used in these DFAFC consists of carbon supported platinum nanoparticles with a sub-monolayer of bismuth (Pt/C-Bi).[2] Over time, bismuth is oxidized and lost from surface resulting in deactivation of the catalyst nanoparticles, which leads to the DFAFC losing performance.[3] Bismuth at moderate Pt surface coverages promotes formic acid adsorption in the CH-down orientation through a combination of the third-body (steric) and electronic effects. When formic acid adsorbs in the CH-down orientation the direct reaction pathway is promoted bypassing the formation of strongly adsorbed reaction intermediates. The overpotentials associated with the direct reaction pathway are minimal, thereby elevating the power output of the DFAFCs. The goal of this project is to explore stable alternative adsorbates to replace bismuth in order to maximize power density and durability of DFAFCs. Three-electrode electrochemical studies are performed on a polycrystalline Pt disk working electrode in 0.1M HClO4. Initial studies with citrate have demonstrated strong surface adsorption to Pt. The cyclic voltammograms in Figure 1 demonstrate that citrate blocks hydrogen adsorption/desorption sites on Pt and coverage is tailorable to that of a submonolayer of citrate. Linear sweep voltammetry in formic acid shows minimal electro-oxidation performance on pure Pt and a full monolayer of citrate. However, for a submonolayer of citrate the activation overpotential is reduced to 0.2 V vs. RHE due to the significant contribution to the direct reaction pathway.

Direct Formic Acid Fuel Cell: Anode Flow Field Designed Two-Phase Removal of Carbon Dioxide

Direct Formic Acid Fuel Cells (DFAFC) are a potential substitute in portable power devices surpassing the capacity of conventional batteries in everyday items such as cell phones and laptops. The challenge of maintaining high liquid phase formic acid (FA, HCOOH) concentrations within the catalyst layer at high current densities is due to the gaseous by-product carbon dioxide formation (HCOOH→ CO2 +2H+ + 2e-). The two-phase FA/CO2 results in mass transport limitations. Previous studies have shown enhanced current density performance when the anode flow field is designed to flow the FA in a singular serpentine pattern[1], and the gaseous CO2 is removed through a semi-permeable separator near site of formation[2]. Fig.1 shows the current serpentine anode flow field’s geometry in ANSYS Fluent. The CO2 forms along the diffusion media//anode catalyst layer and disperses through the semi-permeable layer, after traversing the flow channel. The initial flow field prototype with a semi-permeable separator has issues with liquid FA break through. Improved sealing surface designs were investigated to improve the DFAFC’s efficiency. Mass transport of CO2 in the current semi-permeable anode flow field design results in a “barrier” of higher velocity in between the layers, Fig. 1. In addition, an eddy current appears at the point of entrance into the chamber, potentially re-circulating the CO2 bubbles and hindering removal. Further modifications of the anode flow field, based on the present Computational Fluid Dynamics (CFD) model, are underway to eliminate the barrier and remove the eddy. The objects of the CFD modeling is to realize needed flow distribution improvements on future anode flow field, resulting in a higher rate of CO2 mass transport through the semi-permeable layer. Experimental validation of prototypes will be performed on the resulting model driven design optimizations. [1] Limjeerajarus, Nuttapol, and Patcharawat Charoen-Amornkitt. "Effect of Different Flow Field Designs and Number of Channels on Performance of a Small PEFC." International Journal of Hydrogen Energy, 2015, 40, 7144. [2] S. Saeed, A. Pistono, J. Cisco, C. S. Burke, M. Mench, C. Rice, Fuel Cells, 2017, 17, 48. Figure 1

(Invited) Direct Formic Acid Fuel Cells Anode Optimization: Flow Fields and Catalysts

Direct formic acid fuel cells (DFAFCs) offer an efficient and compact electrochemical conversion technology to power portable electronic devices ranging from sensors to unmanned surveillance vehicles. Liquid fuel cells are desirable for portable applications due to their ease of liquid refueling and the minimal incorporation of system fail safes for handling, as compared to compressed gasses. Directly compared to other liquid fuels, formic acid has minimal parasitic losses due to (i) efficient anodic overpotentials and (ii) cathodic depolarization due to low fuel crossover.[1]The anodic overpotentials are reduced in the presence of efficient catalysts that enhance the fraction of formic acid that is electro-oxidized via the direct non-strongly adsorbed reaction intermediate pathway,[2] while most liquid fuels are plagued with strongly adsorbed carbon monoxide reaction intermediates that require high parasitic overpotentials. Fig 1 compares the formic acid overpotential on a platinum-ruthenium (PtRu) alloy catalyst through the indirect electro-oxidation pathway and carbon supported platinum catalyst decorated with a submonolayer of bismuth (Pt/C-Bi) promoting the direct electro-oxidation pathway. Two short comings incurred in a DFAFC are (Part 1) durability of the catalyst and (Part 2) efficient removal of the CO2-byproduct.[3] Part 1 – The Bi, at 54% of a monolayer coverage, promotes the direct electro-oxidation pathway by the ‘third-body’ effect and adsorption in the CH-down orientation. Alternative adsorbates to Bi are being sought that are strongly adsorbed to the Pt surface and enhance formic acid electro-oxidation through the direct reaction pathway. Stability of the adsorbate during operation and idle will be a key parameter in down selection. Part 2 – The removal of CO2 is imperative to maintain elevated formic acid concentration both in the anode flow field and at the catalyst interfaces within the 3-dimensional anode catalyst layer. The limited crossover of formic acid to the cathode permits the cell to be operated in the presences of neat fuel concentrations. Previously in the Rice group, it has been shown that DFAFC performance is strongly impacted by catalyst layer porosity via either swelling of the catalyst layer[4] or using a pore former to create larger pore structures in the catalyst layer[5]. As the DFAFC operates under higher loads, additional CO2 must be removed through a typical single serpentine flow field, resulting in non-uniformed fuel distribution at the catalyst interface due to two-phase flow. Recent work on advanced electrically conductive selectively gas permeable anode flow field (SGPFF) designs have resulted in efficient removal of CO2 perpendicular to the active area near the location where it is formed in the catalyst layer.[6] Fig 2 shows the potentiostatic hold performance (0.3V) in a dead-ended flow field operation for a standard flow field vs. the SGPFF using PtRu/C as the anode catalyst. Acknowledgements: We gratefully acknowledge support of this work by the NSF-funded TN-SCORE program, NSF EPS-1004083, under Thrust 2 and the Center for Manufacturing Research at Tennessee Tech University.

Voltage Inversion Caused by Self-organized Oscillations in a Direct Formic Acid Fuel Cell

Voltage Inversion Caused by Self-organized Oscillations in a Direct Formic Acid Fuel Cell

Evaluation of the Dimensional Stability and Conductivity of PEM in Aqueous Solutions of Formic Acid for Use in Dfafcs

Global energy consumption is one of the greatest problems humanity is facing and the need for viable and environmentally friendly alternative energy sources is rising. One of these alternative technologies is Direct Formic Acid Fuel Cells (DFAFCs) a promising alternative energy source for the constantly increasing energy demand; they have major potential for use in portable devices as they can perform extremely well at ambient temperatures and have a low environmental footprint. Due to the low permeability of formic acid through the polymer exchange membrane (PEM) it allows work at higher concentrations leading to higher energy production compared to other fuel cells. Working under similar operating conditions DFAFCs can generate power densities of 233 mW/cm2 outperforming Direct Methanol Fuel Cells (DMFCs) with power densities of 53 mW/cm2 (1). However, no fundamental studies about the intrinsic conductivity and dimensional stability of PEM have been carried out whilst under use of formic acid with the purpose of understanding how PEM behave under such highly acidic conditions. This is vital for understanding the long term performance and durability of such fuel cells, should they be used on a wider scale. The studies carried out have examined how the PEM, including Nafion 115,117,211 and 212, behave and perform under varying acidic conditions. For the dimensional stability study optical analysis was carried out to determine the changes occurring in-situ to the material. In addition, determining changes in resistance using impedance spectroscopy allows for the selection of the most efficient membrane configuration for optimal cell operation. Previous research has shown that Nafion with a lower equivalent weight has an increased hydrophilic region, compared with membranes with higher equivalent weight. Using this relationship to understand the performance of Nafion suggests that a higher hydrophilic region leads to deformity by the formic acid on the membrane. We have observed this as a change in the dimension of the membrane in only one direction; a change that is not observed when the membrane is immersed in water alone, where the changes in the dimensions are uniform in two directions. There are two possible causes of this; firstly by the production process of the membrane or that a change is taking place in the hydrophobic regions the continuous semi- crystalline TFE structure of the material. In this work we will explain the cause of the deformation. 1. 2-D Crystals Significantly Enhance the Performance of a Working Fuel Cell. Stuart M. Holmes*, Prabhuraj Balakrishnan, Vasu. S. Kalangi, Pulickel M. Ajayan, Xiang Zhang, Marcelo Lozada-Hidalgo and Rahul R. Nair. 27.09.2016., Advanced Energy Materials.

Oscillatory Reaction Rates in a Direct Formic Acid Fuel Cell (DFAFC)

Formic acid has been studied as a promising fuel for its direct oxidation in fuel cells since, in comparison with other organic molecules, it is more easily oxidized to CO2, has a high thermodynamic voltage and fewer problems associated with crossover [1]. It is accepted that the electro-oxidation of formic acid on platinum proceeds through parallel reaction pathways, including an indirect path through carbon monoxide poisoning, the active intermediate (or formate) pathway and the direct pathway [2]. From another point of view, the electro-oxidation of formic acid on Pt and on Pt-group metals is a typical system showing periodic oscillations. Basically, the mechanism that gives rise to this type of oscillatory dynamics is the interplay between the adsorption isotherm of a catalytic poison, for example θCO, and of oxygenated species, θOH, both of which are potential dependent [3]. A key question underlying this dynamics is how it can affect the efficiency of a DFAFC. The purpose of this study was to evaluate the performance of a DFAFC under oscillatory regime. The experiments were performed using the typical setup of a unit cell, with a special approach (hydrogen on the cathode) that allows reading the anodic overvoltage directly. The conditions were: Pt/C (50 wt%) was used as anodic and cathodic catalysts with a metal loading of 1 mgPt cm-2. The anode was fed with 8 mol L-1 of HCOOH and the cathode was fed with H2. The unit cell (≈ 4.6 cm2) was operated at 30oC under atmosphere pressure. Figure 1 exhibits the current-potential curves obtained under potentiostatic and galvanostatic control modes for the electro-oxidation of formic acid and the theoretical curve for oxygen reduction. It is worth noting that the high overpotential required for the oxygen reduction and for the formic acid oxidation on Pt drastically reduces the DFAFC voltage, as it does for all fuel cells, given the sluggish kinetics. However, during the slow galvanodynamic sweep, spontaneous voltage oscillations emerge and this kinetic instability periodically decreases the anodic overpotential. This fact is interesting since the oscillations increase the average cell voltage and could result in the deceleration of long-term surface deactivation [4]. It also testifies to the importance of evaluating its dynamics to improve the fuel cell efficiency. The occurrence of such oscillatory behavior during the operation of a Direct Methanol Fuel Cell (DMFC) has been report, however, due to the small amplitude and waveform of the oscillations that takes place during the methanol electro-oxidation, no net improvement was observed in this system [5]. Although, a decrease in long-term instabilities can still play an important role. Probably, the self-cleaning process is more efficient for formic acid oxidation than that for methanol due to its larger amplitude and also because during a cycle the anodic overpotential remains longer at lower values [4]. Here we report a self-organization process observed in a DFAFC and its influence on the device efficiency. It was observed that at certain moments the anodic potential is lower than that on a steady state and this phenomena together with a self-cleaning process could improve the overall fuel cell performance. Acknowledgements J.A.N. and H.V. acknowledge São Paulo Research Foundation (FAPESP) for the scholarship (grant #2015/09295-9) and financial support (grants #2012/21204-0, and #2013/16930-7). H.V. (#306151/2010-3) also acknowledges Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support.

Improvement of Different PEM Fuel Cell Perfromance By Using Graphene Oxide and N-Doped Graphene Produced By Electrochemical Exfoliation of Graphite in the Micro Porous Layer

Fuel cells have attracted great attention in recent times as a promising replacement for traditional engines. They offer numerous benefits such a high power density, compactness, lightweight and zero or low greenhouse emissions. There are different types of fuel cells, which transform the energy of a chemical reaction directly into electrical energy. One of the most attractive and effective, particularly, in terms of transportation applications are Proton Exchange Membrane Fuel Cells (PEMFC). The Membrane Electrode Assembly (MEA) is the most important part of a fuel cell. The MEA is composed of two electrodes (anode and cathode), and a polymer exchange membrane. Each electrode is composed of different layers, the gas diffusion layer (GDL), Micro Porous Layer (MPL) and the catalyst layer (CL). MPL is important due to its role in efficient electron transfer process and effective transport of reactants towards the catalyst layer and removal of products from the MEA. The MPL also serves an electrical contact link between the carbon paper and the catalyst layer. Hence enhancing electrical contact by using highly conductive materials is expected to reflect in improved performance. Great efforts have been made to research of different materials which have good electron conductivity to improve the reaction kinetics, as they facilitate easier travel of electrons in the electron pathway, thereby increasing the performance. Graphene oxide (GO) is considered as a good proton conducting material, at the same time it is impermeable to dry gases and electrons. N-doped graphene has even used as an efficient electrode material in a variety of applications such as catalyst for oxygen reduction reactions in PEMFC, lithium-ion batteries and supercapacitors [1]. Because of their properties, GO and N-doped graphene can be considered as good candidate materials to use in a MPL. Several graphene preparation methods have been developed, such as chemical vapour deposition (CVD), arc discharge, segregation growth or Hummers method. However, the requirements of expensive equipment used, extreme reaction conditions and the usage of highly toxic chemicals are some of the inconvenient that these techniques present. Electrochemical exfoliation of graphite has been presented as a green and cost-effective approach for producing high quality of graphene in high yield using simple equipment [1-3]. In this work, GO and N-doped graphene have been prepared by electrochemical exfoliation of graphite in aqueous inorganic salt and ammonium nitrate as electrolyte. This process is performed in a two electrode system using platinum as the counter electrode and graphite sheet as a working electrode under neutral pH conditions. A power supply is used to apply a voltage of 10V. Different MEAs are been assembled using the GO and N-doped graphene in the MPL. The enhanced performance of these MEA’s in different fuel cell such as DMFC, Hydrogen Fuel Cell (PEMFC) and Direct Formic Acid Fuel Cell (DFAFC) will be described. We have shown that the replacement of the carbon material used in the MPL by reduced graphene oxide (rGO) and (GO) on the cathode side can provide significant improvement on the power density of up to 84%.

Stationary and Damped Oscillations in a Direct Formic Acid Fuel Cell (DFAFC) using Pt/C

Herein, we report damped and stationary oscillations during Formic Acid oxidation (FAO) under galvanostatic control in a Direct Formic Acid fuel cell (DFAFC). Using Pt/C catalyst in a practical DFAFC, the anodic electrode are allowed to rise its potential up to 600mV, at the most, which, in turn leads to solely presence of damped oscillations during FAO. When employing dynamic hydrogen electrode (DHE) for measuring anodic voltage values, in a half-DFAFC, larger potential accessed with anodic gas diffusion electrode (GDE) undergoing FAO. With it, stationary oscillatory patterns are observed with an average potential equal to 1V and with maximum potential equal to 1.25V. Such high maximum-potential oscillations are reproduced in experiments with rotating disc electrode (RDE), indicating, thus, that such behaviour derives from chemical mechanism rather than possible spatial coupling in a DFAFC. And, to explained it, we suggest to add to current oscillatory mechanism for FAO the steps originally proposed by Tian and Conway (2005) that involves direct chemical reaction of surface oxide with the bulk formic acid (or formate). Finally, we found that maximum potential of stationary oscillations is controlled by bulk formic acid diffusion, thus, a DFAFC with improving FA diffusion on the GDE would allow the presence of stationary oscillation in practical conditions, which is wanted given the improved efficiency as elucidated with the help of overvoltage analysis.

Highly Effective PdCu Electrocatalysts Supported on Polyelectrolyte Functionalized Titanium Dioxide for Direct Formic Acid Fuel Cells

Highly Effective PdCu Electrocatalysts Supported on Polyelectrolyte Functionalized Titanium Dioxide for Direct Formic Acid Fuel Cells

The Study of Pt and Pd based Anode Catalysis for Formic Acid Fuel Cell

Detailed investigation of HCOOH electro-oxidation started about five decades ago, with the advent of modern potentiodynamic techniques, driven initially by the purpose of elucidating some of the most interesting and challenging electrode kinetic problems. Many pioneering works that withstood the test of time and the continuous sophistication of surface electrochemistry techniques were published in the 1960s. Stimulated results were obtained, such as: (i) phenomenological interpretation of anodic polarization curves (e.g., Determination of Tafel parameters), HCOOH oxidation on Pd and Pt catalysts; (ii) discovery of the catalytic effect with respect to Pt and Pd for HCCOH oxidation; (iii) investigation of the potential dependent adsorption of HCOOH on Pt and Pd catalysts which are accompanied by a dual pathway mechanism and (iv) formic acid concentration, temperature effects and crossover of nafion membrane.

Advanced Selectively Gas Permeable Anode Flow Field Design for Removal of Carbon Dioxide in a Direct Formic Acid Fuel Cell

AbstractDirect formic acid fuel cells (DFAFCs) are electrochemical energy conversion devices well suited to power portable electronics, if researchers can harness their high theoretical efficiencies and address durability issues. To improve DFAFC efficiency, the mass transport of formic acid to the anode catalyst layer must be improved. Conventional serpentine anode flow field designs limit CO2 product removal through a single flow field channel hindered by two‐phase flow. Presented herein is an advanced electrically conductive, selectively gas permeable anode flow field (SGPFF) design that allows for efficient removal of CO2 perpendicular to the active area near the location where it is formed in the catalyst layer. The anode plate design consists of two mating flow fields separated by semi‐permeable separator to allow diffusive transport of CO2. Herein, performance differences between a conventional liquid‐fed flow field and an advanced SGPFF design are examined. Polarization curves revealed a 10% increase in performance of the SGPFF with confirmation of CO2 removal within the gaseous side. A potential hold test at 0.3 V showed that the SGPFF sustained power generation for 9.5 times longer than that of the conventional anode flow field design in a dead‐ended configuration, demonstrating the fixture's potential for sustained power generation.

Power Generation Characteristics of the Direct Formic Acid Fuel Cell Using Silica Containing Carbon Nanofiber as the Anode Supports

Direct formic acid fuel cells, DFAFCs, have received considerable attention due to their higher power density in the direct liquid fuel cells. Recently, 550 mW/cm2 of power density at 30 oC was reported by Chan et al. using Pd–Ni2 P/C catalyst for DFAFC anode [1]. In order to obtain the higher power density, the operation temperature of DFAFC should be elevated since anode and cathode reaction kinetics increases with the increasing operation temperature, however, it has been known that the power density of DFAFC above 50 oC showed plateau with the increasing temperature. As a reason of the plateau in the power desnity above 50 oC, the increase of the mass transport loss was considered [2]. Therefore, controlling the mass transport in the catalyst layer is one of the key factor to obtain high power density. In this context, the silica embedded carbon nanofiber, SECNF, support for DFAFC anode have been suggested in this study. By using SECNF as a catalyst support, both of the high porosity catalyst layer which can enhance the mass transport rate in the catalyst layer and the high catalystic activity due to the support metal effect of the silica have been expected. It was found that the formic acid oxidation reaction activity significantly increased by using SECNF as a support of Pd comparing to conventional Pd/CNF and Pd/C due to the support effect of the SiO2. Moreover, the high porosity anode electrode could be successfully fabricated by using Pd/SECNF. On the other hand, the power density of DFAFC was not enhanced due to thick catalyst layer. In the presentation, the effect of the porosity and thickness of catalyst layer on the anode mass transport loss and power generation characteristics will be discussed in detail. Reference [1] J. Chang, L. Feng, C. Liu, W. Xing, and X. Hu, Angew. Chemie Int. Ed., 53, 122–126 (2014). [2] T. Tsujiguchi, F. Matsuoka, Y. Hokari, Y. Osaka, and A. Kodama, Electrochim. Acta, 197, 32–38 (2016)

Electrochemically Fabricated Binary Alloy Catalysts for CO2-C1 Fuel Inter-Conversion

Electrochemical reduction of carbon dioxide to useful chemical has been studied as a promising method to utilize CO2. This method can selectively produce a variety of useful chemicals (e.g. carbon monoxide, formic acid, methane, and other hydrocarbons) according as reaction condition such as types of electro-catalysts, electrolytes, operation voltage, and so on [1,2]. In this study, we selected formate as a target product because it has various advantages as a feed stock chemical. Formate is produced by the electrochemical reduction of the CO2 and the formate, after treatment to form formic acid, will be used as fuel for Direct Formic Acid Fuel Cell. Particularly in the case of CO2-based unitized re-generative fuel cell, the inter-conversion reaction between CO2-C1 fuels is important. Therefore, we develop a catalyst that can be used in both sides reaction; the electrochemical conversion of CO2 to formate and the oxidation of formic acid [3]. In this case, it is most important to develop bi-functional catalysts that have activities for both reactions. In addition, high selectivity and activity to CO2 reduction as well as reduced amounts of noble metal loading for the formic acid oxidation reaction are also desired. The catalysts were made by co-electrodeposition of noble metal and post-transition metal to form binary alloy catalysts. Electrodeposition was performed at a constant deposition potential in a 3-electrode cell containing metal precursors, supporting electrolyte, and complexing agent. For some cases, thermal annealing was performed to enhance the characteristics of the fabricated catalysts. The alloy catalysts were characterized with EDS, SEM and XRD. The electrochemical reduction of carbon dioxide was performed and the produced amounts of formate were measured with HPLC. Formic acid oxidation was also performed with CV using the same catalysts. The activities to both reactions were characterized according to the alloy composition, morphologies, and other physic-chemical properties. In conclusion, certain composition of the alloy catalysts exhibited the significant activities to both reactions simultaneously.

Power Generation Characteristics of the Direct Formic Acid Fuel Cell Using Silica Containing Carbon Nanofiber as the Anode Supports

In order to prepare high Pd containing Pd/SECNF (SiO2 containing carbon nanofiber) catalyst, which showed high formic acid oxidation reaction activity, the effect of the time and frequency on the ultrasonication before the chemical reduction process was investigated. It was found that 45 kHz and 45 min was the optimum condition. Based on this condition, Pd/SECNF containing 80 wt% of Pd was successfully prepared. Using this catalyst for the DFAFC anode, power generation characteristics was investigated. It was found that the performance was similar to the conventional DFAFC using Pd/C for anode catalyst although the catalytic activity of Pd/SECNF was higher than that of Pd/C. This is due to the high anode mass transport resistance in the anode catalyst layer in the case of Pd/SECNF.

Facile Synthesis of Carbon‐Supported Ultrasmall Ag@Pd Core‐Shell Nanocrystals with Superior Electrocatalytic Activity for Direct Formic Acid Fuel Cell Application

AbstractTo design electrocatalysts with excellent performance, morphology, composition and structure is a decisive influential factor. In this work, ultrasmall Ag@Pd core‐shell nanocrystals supported on Vulcan XC72R carbon with different Ag/Pd atomic ratios are synthesized via a facile successive reduction approach with formaldehyde and ethylene glycol as reducing agents, respectively. The Ag‐core/Pd‐shell nanostructures are revealed by high‐resolution transmission electron microscopy (HRTEM). Ag@Pd core‐shell nanocrystals possess a narrow size distribution with an average size of ca. 4.3 nm. In comparison to monometallic Pd/C and commercial Pd black catalysts, such Ag@Pd core‐shell nanocrystals display excellent electrocatalytic activities for formic acid oxidation, which may be due to high Pd utilization derived from the formation of Ag@Pd core‐shell nanostructure and the strong interaction between Ag and Pd.

에틸렌글리콜 양 조절에 의해 제조된 팔라듐구리 촉매를 이용한 개미산연료전지 성능평가

에틸렌글리콜 양 조절에 의해 제조된 팔라듐구리 촉매를 이용한 개미산연료전지 성능평가

Effect of Reactant Flow Rate and Operation modes on Direct Formic Acid Fuel Cell (DFAFC) Performance

Background/Objectives: The main focus of this research is to study the effects of reactant flow, i.e. formic acid and oxidant, and operation mode, i.e. passive, semi-passive or active conditions, on the Direct Formic Acid Fuel Cell (DFAFC) performances. Methods/Statistical Analysis: A single cell DFAFC with 5 cm 2 electrode is used in this study. The DFAFC is operated with 10 M of formic acid concentration under four modes of reactant supply: air breathing, air flowing(80 to 600 mL min -1 ), oxygen flowing (10 to 100 mL min -1 ) at the cathode, and formic acid flowing (2 to 15 mL min -1 ) at the anode to investigate their effects on cell performance. Findings: It is obtained that the DFAFC performances are affected by oxidant types, i.e., air and oxygen, flow rate, and the mode of operation. In passive operation, the maximum power density is obtained at 2.95 mW cm -2 . The highest performance is achieved in semi-passive using 50 mL min -1 of oxygen with maximum power density of 10.92 mW cm -2 . Meanwhile, for semi-passive using air flow condition at 400 ml min -1 shows a maximum power density at which 8.89 mW cm -2 . For active operation, the highest performance is obtained using 6 mL min -1 with a maximum power density at 8.52 mW cm -2 . Application/Improvements: The semi-passive operation with oxygen could improve the DFAFC performances, and hence the DFAFC could be used as an energy source for electric and electronic applications.

Preparation and Evaluation of Nickel Oxide-Carbon Nanotube Supported Palladium as Anode Electrocatalyst for Formic Acid Fuel Cells

Preparation and Evaluation of Nickel Oxide-Carbon Nanotube Supported Palladium as Anode Electrocatalyst for Formic Acid Fuel Cells