Formic Acid Electrooxidation Research Articles

Hydrogen evolution reaction and formic acid oxidation by decorated nanostructural Pt/Pd on a copper-filled nanoporous stainless steel

In this work, a 304 stainless steel (SS) was anodized to prepare nanoporous SS (NPSS) with an average size of about 75 nm and then filled with copper (Cu/NPSS) using pulsed electrodeposition method. Afterward, a nanostructural Pt and Pd film was deposited by galvanic replacement (GR) on the Cu/NPSS to prepare modified electrode (PtPd/Cu/NPSS) for hydrogen evolution reaction (HER) and formic acid electrooxidation (FAO). The electrocatalytic activity of the modified electrode and its structural characterization have been studied by voltammetric methods, electrochemical impedance spectroscopy (EIS), inductively coupled plasma optical emission spectrometry (ICP-OES), and field emission scanning electron microscopy (FESEM). The results show that the nanostructural Pt1Pd1/Cu/NPSS composition, with low Pt loading and suitable stability, has a good electrocatalytic performance toward HER (EOnset = + 12 mV vs. NHE) and FAO (EOnset = −180 mV vs. NHE). For HER observed a high mass activity of noble metals (87.54 mA cm−2μg Pd+Pt −1 ) in comparison with Pt deposited Cu/NPSS (41.5 mA cm−2 μg Pt −1 ) at the same applied potential of − 0.25 V versus NHE. Also, the fabricated electrocatalysts with more electrochemically active surface area in comparison with Pd/Cu/NPSS and Pt/Cu/NPSS revealed more resisting to the poisoning components and good stability for FAO.

An effective Pd@Ni-B/C anode catalyst for electro-oxidation of formic acid

The Pd@Ni-B/C catalysts were prepared by using Ni-B/C with different amounts of Ni-B alloys as supports. The structure, morphology and element valence state of these catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The electro-catalytic performance of these catalysts for formic acid oxidation was investigated using cyclic voltammetry (CV), chronoamperometry (CA) and CO stripping experiments. It was found that an appropriate amount of Ni-B alloys plays an important role in enhancing catalytic activity and resistance to CO poisoning and improving stability of Pd based catalysts, all of which imply that Pd@Ni1.61B0.0199/C is promising for probable applications in direct formic acid fuel cell field.

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.

Direct Formic Acid Electro-Oxidation on Pt Doped and Undoped La1-xSrxCoO3: Activity Suppression due to Proton Reduction Reaction

Combustion synthesized Pt-doped and undoped La1-xSrxCoO3 are utilized for formic acid electro-oxidation. Cyclic-voltammetry (CV) during formic acid electro-oxidation demonstrates that the oxidation current initially increases and then decays to zero on both the catalysts. This implies that the HCOOH possibly has some poisoning effect on the catalysts. Both materials show a unique reduction peak in the oxidation scan right after the addition of HCOOH in the electrolyte, demonstrating a reduction process in the oxidation cycle. When HCOOH is replaced by potassium formate, the reduction peak is found absent. Further, significant increase in the current is observed in the case of La1-xSrxCoO3. This confirms that the protons which are generated during the electro-oxidation of HCOOH are reduced on the catalyst's surface generating the reduction peak in the CV. This process suppresses the counter-reaction to diminish the current. Instead of protons, K+ ions are generated with potassium formate which greatly prevents the proton reduction reaction and leads to the formate ion oxidation. Only CO2 was evolved during the electro-oxidation which was confirmed through gas chromatography. Further investigations reveal that apart from proton reduction reaction, Pt-doped La1-xSrxCoO3 gets poisoned in presence of CO2 also; the main oxidation product of both HCOOH and KCOOH.

Kinetic Study of Formic Acid Electrochemical Oxidation on Supported Pd Based Electrocatalysts

Developing high performance catalyst based on Pd/C catalyst is critical in investigating and commercializing direct formic acid fuel cell. The improvement of the electron-transfer rate of novel catalysts could solve the sluggish reaction kinetics of formic acid electro-oxidation reaction in some extent. We have demonstrated that phosphotungstic acid (PWA) modified Pd/C catalyst could improve the electro-oxidation activity toward formic acid. In this paper, the electrochemical oxidation reaction kinetics of PWA modified Pd/C catalyst were studied by cyclic voltammetry (CV), Tafel polarization, electrochemical impedance spectroscopy (EIS) and rotating disc voltammetry (RDV) at different scanning rates and temperatures. The results showed that smaller apparent activation energy, charge transfer resistance and Tafel slope of formic acid electro-oxidation from Pd/PWA–C electrode catalyst was obtained, which indicated better electrocatalytic kinetics by PWA modification. The rate-determining step of formic acid electro-oxidation is diffusion process and reaction paths are different with potential. The larger diffusion coefficients of Pd/PWA–C electrode catalyst was verified by CV, EIS and RDV, respectively. With the help of electrochemical measurements, it is concluded that PWA modified Pd/C catalyst has better electrocatalytic activity and faster kinetic performance for formic acid electro-oxidation.

Controlled Synthesis of Hierarchical Pd Nanodendrites and Their Electrocatalytic Properties.

Well-defined hierarchical Pd nanodendrites with (111) surface were successfully synthesized with Pd(acac)2 as a precursor, polyvinylpyrrolidone (PVP) as a stabilizer, CO as a reducing agent in the presence of appropriate amounts of NaAc and oleylamide (OAm) at 100 °C for 3 h under atmospheric pressure. OAm played an important role in controlling the growth of the hierarchical dendritic nanostructures of the final products. The formation of the hierarchical Pd dendrites was ascribed to the OAm-confined growth from the tips along 〈111〉 axis directions. This kind of hierarchical Pd nanodendrites exhibited an enhanced electrocatalytic activity for the electro-oxidation of formic acid compared with Pd black.

Structure Sensitivity of Formic Acid Electrooxidation on Transition Metal Surfaces: A First-Principles Study

Formic acid presents several advantages for use as a fuel in fuel cells. We present a first-principles based analysis of electrooxidation trends for formic acid on the close-packed facets of eight fcc metals: Au, Ag, Cu, Pt, Pd, Ni, Ir, and Rh, and four hcp metals: Co, Os, Ru, and Re. To explore the structure sensitivity of this reaction on the fcc metals, we also studied the open (100) facet of these eight metals. We find that the open facets of Au, Ag, Cu, Pt, and Pd are more energy-efficient (i.e. require less overpotential) for formic acid electrooxidation when compared to their close-packed facets. The opposite is true for the stronger-binding metals: Ni, Ir, and Rh. Using the free energy of adsorbed CO* and OH* as reactivity descriptors, we cast the thermochemistry of the reaction network into phase diagrams showing regions of rate-determining steps, together with their calculated free energies. This allows the identification of bimetallic alloys, potentially possessing improved electrocatalysis for formic acid electrooxidation, compared to Pt or Pd. We discuss the need for anode catalysts for direct formic acid fuel cells (DFAFCs) to diminish CO* poisoning, by promoting the formation of formate instead of carboxyl intermediate.

PtAl truncated octahedron nanocrystals for improved formic acid electrooxidation.

We successfully obtained truncated octahedron PtAl alloy nanocrystals (∼10 nm) via a facile one-pot strategy. The PtAl nanocrystals exhibited enhanced activity in formic acid electrooxidation compared to commercial Pt/C, which could be ascribed to the large density of defects on the surface as well as the synergy between Pt and Al.

Synergism of molybdenum nitride and palladium for high-efficiency formic acid electrooxidation

In this paper, a coupled Mo2N–Pd structure with intimate contact and strong interaction located on reduced graphene oxide (Pd–Mo2N/rGO) was successfully designed for high-efficiency formic acid oxidation. The Pd–Mo2N/rGO catalyst shows superior activity to Pd/rGO and Pd/VC, respectively. In addition, Pd–Mo2N/rGO exhibits enhanced CO tolerance and good stability.

Pd/WO3/C nanocomposite with APTMS-functionalized tungsten oxide nanosheet for formic acid electrooxidation enhancement

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

Electrooxidation of Formic Acid Using Pt Nanoparticles Supported on Conducting Poly(Vinylferrocene) Polymer Support

Y akit olarak metanolun toksisite ve dusuk elektrokatalitik yukseltgenme hizi gibi bazi dezavantajlari oldugu icin yakit pili uygulamalarinda alternatif yakitlar ilgi cekmektedir. Diger taraftan, tasima ve kullanim kolayliginin yani sira yuksek teorik acik devre potansiyeli gibi ozellikleriyle dikkat ceken formik asit metanole alternatif olarak ortaya cikmaktadir. Poli vinilferrosen destekli platin Pt/PVF dogrudan formik asit yakit hucrelerinde kullanim icin gelecek vadeden bir katalizordur. Bu calismada Pt/PVF katalizor sistemiyle formik asitin elektroyukseltgenmesi ile metanol ve formik asitin karsilastirilmasi yer almaktadir. Taramali elektron mikroskobu goruntulerine gore, Pt tanecikleri polimer destek uzerinde duzgun dagilmistir. Pt/PVF katalizoru formik asit yukseltgenmesi icin yuksek katalitik aktivite gostermistir. Ayni kosullarda metanolun elektroyukseltgenmesiyle karsilastirildiginda, formik asit icin daha iyi sonuclar elde edilmistir

Ultrathin Pt–Zn Nanowires: High-Performance Catalysts for Electrooxidation of Methanol and Formic Acid

Herein, we have developed a Zn2+ ion induced reduction strategy (ZIRS) for synthesizing ultrathin Pt–Zn nanowires (NWs) with average size of ∼2.2 nm. The precise selection of solvent and the addition of ZnCl2 precursor are of crucial significance to preparing bimetallic NWs. The NWs exhibited electrocatalytic performance compared with commercial catalysts, such as electrooxidation of methanol (MOR) and formic acid (FAOR). Moreover, the prepared Pt–Zn NWs can be adopted as a template to prepare Pt-based trimetallic ultrathin NWs.

Facile Construction of N-Doped Graphene Supported Hollow PtAg Nanodendrites as Highly Efficient Electrocatalysts toward Formic Acid Oxidation Reaction

The lack of cost-efficient catalysts for the electrooxidation of fuel in the anodic electrode has been a major barrier for the practical large-scale commercial application and hence needs to be optimized. Tuning the morphologies and structures of Pt-based bimetallic nanostructure plays a key role in controlling its interaction with reactants, and thus affects its electrocatalytic efficiency. In this regard, endowing the nanocatalysts with both of high surface active areas and controlled facets through modifying their surface compositions and morphologies can significantly enhance their electrocatalytic performances. To this end, we herein demonstrate a facile wet-chemical method to successfully construct the N-doped graphene supported hollow PtAg nanodendrites under the assistance of ultrasonic treatment. More importantly, the resulting N-doped graphene supported hollow PtAg nanodendrites show high performance for the electrooxidation of formic acid with the mass and specific activities of 1258.5 mA mg–1 ...

FePt nanoalloys on N-doped graphene paper as integrated electrode towards efficient formic acid electrooxidation

Pt-based bimetallic alloys have attracted intensive interests as highly efficient and stable heterogeneous catalysts for fuel cell applications, and searching flexible free-standing nanomembranes has been on the research focus because of their promising applications in catalysis, nanoelectronics, batteries, and sensing. Herein, a flexible free-standing paper composed of FePt alloy nanoparticles on nitrogen-doped paper (FePt–NG paper) has been developed as integrated electrode towards electrocatalytic oxidation of formic acid. It is found that, N doping is beneficial for the well dispersion of FePt nanoparticles on NG paper. The synergistic effect between Fe and Pt, as well as N doping effect simultaneously assures the improved catalytic activity of FePt–NG paper, making it the promising flexible electrode for application in fuel cell system. Moreover, the synthesis strategy could be used for the construction of other free-standing electrode towards catalysis, sensing, and battery applications.

Fe2P as a novel efficient catalyst promoter in Pd/C system for formic acid electro-oxidation in fuel cells reaction

Developing catalyst promoter for Pd/C catalyst is significant for the catalytic ability improvement in energy transfer related electrochemical reactions. Herein, we demonstrate Fe2P as an efficient catalyst promoter in Pd/C catalyst system for formic acid electro-oxidation in fuel cells reactions. Adding Fe2P in the Pd/C catalyst system greatly increases the performances for formic acid oxidation by 3–4 times; the CO stripping technique displays two kinds of active sites formation in the Pd-Fe2P/C catalyst system coming from the interaction of Pd, Fe2P and Pd oxide species and both are more efficient for formic acid and CO-species electrooxidation. The smaller charge transfer resistance and Tafel slope for formic acid oxidation indicate the improvements in kinetics by Fe2P in the Pd-Fe2P/C system. The nanostructured hybrid units of Pd, Fe2P and carbon are evidently visible in the high resolution microscopy images and XPS technique confirmes the electronic effect in the catalyst system. The promotion effect of Fe2P in the catalyst system arising from the structure, composition and electronic effect changes is discussed with the help from multiple physical and electrochemical techniques. It is concluded that Fe2P as a significant catalyst promoter will have potential application in energy transfer related electrochemical reactions.

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.

WO3/C supported Pd catalysts for formic acid electro-oxidation activity

Pd-WO3/C ternary hybrid was designed as a high-efficient catalyst towards formic acid electrooxidation. WO3/C hybrids were first prepared with two different synthesis order, and then used as the supports to synthesize two kinds of Pd-WO3/C catalysts by a quick and facile microwave-assisted ethylene glycol method. Compared with Pd/C, the catalytic performances of two Pd-WO3/C catalysts towards formic acid electrooxidation are significantly enhanced. We elected the better synthesis order and optimized the best proportion of WO3 and C in the hybrid catalyst. When the mass content of WO3 is 20% of the mass of the support, Pd nanoparticles with narrower particle size distribution are more uniformly dispersed on the surface of WO3/C support than the other counterparts, resulting in the highest performance in terms of activity and stability towards formic acid oxidation among all the samples. The reasons for the performance improvement may be: first, Pd nanoparticles in Pd-WO3/C catalysts are of small size and evenly distributed; second, there may be the catalyst-support interaction between Pd and WO3, substantially improving the catalytic capability of Pd-WO3/C catalysts; finally, the hydrogen spillover effect produced by WO3 significantly expedites the dehydrogenation of formic acid on the surface of Pd-WO3/C.

Stable palladium hydride as a superior anode electrocatalyst for direct formic acid fuel cells

Direct formic acid fuel cells (DFAFCs) are a promising clean power source. To date, palladium (Pd)-based catalysts are the best promising anode catalyst for DFAFCs due to its high anti-poisoning ability and low cost. In this paper, we report a high-efficiency stable PdHx nanocatalyst towards DFAFCs. The PdHx nanocatalysts are prepared by simply treating the commercial Pd black with n-butylamine at relative low temperature (100–200°C). They are extremely stable, and the as-prepared PdH0.43 nanocatalysts show extremely low overpotential for formic acid electrooxidation, with an oxidation peak potential of 0.04V versus SCE (saturated calomel electrode). Meanwhile, the PdH0.43 exhibits as high as 3 times mass activity, 5 times specific activity and great catalytic stability, compared with the untreated commercial Pd black. The present strategy offers a convenient way to boost the performance of Pd nanocatalysts in DFAFCs.

Oxygen adsorption on Pt-Pd nanoclusters by DFT and ab initio atomistic thermodynamics

Monometallic Pt and Pd, and bimetallic Pt-core/Pd12-shell and Pd-core/Pt12-shell were built and geometrically optimized by density functional theory calculations in consideration of oxygen adsorption. The different oxygen adsorption sites on the cluster were considered: top site on one shell atom, bridge site between two shell atoms and hollow site among three shell atoms. For each adsorption site, a few coverages were considered, both oxygen-rich condition and oxygen-poor condition. The pressure-temperature phase diagrams were determined for 13-atom Pt-Pd clusters with adsorbed oxygens in terms of ab initio atomistic thermodynamics method. The most stable phase structure and adsorption of oxygen at certain temperature and pressure were illustrated. Additionally the results showed that the cluster structures were most likely to be changed under oxygen-poor condition. This study is helpful to understand their catalyst processes in a few oxygen-involved reactions such as formic acid electro-oxidation, direct methanol fuel cell, oxygen reduction reaction in fuel cells, oxidation of sulfur dioxide and diesel oxidation and so on.

A General Strategy Assisted with Dual Reductants and Dual Protecting Agents for Preparing Pt-Based Alloys with High-Index Facets and Excellent Electrocatalytic Performance.

Synthesizing noble metallic nanoparticles (NPs) enclosed by high-index facets (HIFs) is challenged as it involves the tuning of growth kinetics, the selective adsorption of certain chemical species, and the epitaxial growth from HIF enclosed seeds. Herein, a simple and general strategy is reported by using dual reduction agents and dual capping agents to prepare Pt-based alloy NPs with HIFs, in which both glycine and poly(vinylpyrrolidone) serve as the reductants and capping agents. Due to the facilely tunable growth/nucleation rates and protecting abilities of the reductants and capping agents, Pt concave nanocube (CNC), binary Pt-Ni CNC, ternary Pt-Mn-Cu CNC, and Pt-Mn-Cu ramiform polyhedron alloy NPs terminated by HIFs as well as other NPs with well-defined morphologies such as Pt-Mn-Cu nanocube and Pt-Mn-Cu nanoflower are obtained with this approach. Owing to the high density of low-coordinated Pt sites (HIF structure) and the unique electronic effect of Pt-Mn-Cu ternary alloys, the as-prepared Pt-Mn-Cu NPs show enhanced catalytic activity toward methanol and formic acid electro-oxidation reactions with excellent stability. This work provides a promising methodology for designing and fabricating Pt-based alloy NPs as efficient fuel cell catalyst.