Electrocatalytic Oxidation Of Formic Acid Research Articles

Efficient formic acid oxidation over gallium oxide incorporated Pd containing electrocatalyst

In this work, a highly efficient Pd catalyst containing gallium oxides supported on reduced graphene oxides has been synthesized by sodium borohydride reduction method for the electro-oxidation of formic acid. The synthesized PdxGay/rGOs display outstanding electrocatalytic activity with considerably higher surface area and improved electrical conductivity during formic acid oxidation as compared to Pd/C. According to the electrochemical results the Pd6Ga4/rGO showed significantly higher electrochemical surface area (102.4 m2/g), improved catalytic activity (86 mA/cm2), smaller Tafel slope value (121 mV dec−1) and excellent durability during the electrocatalytic formic acid oxidation. Th higher turnover frequency of Pd6Ga4/rGO (4.2 × 10−1) further validates its better electrocatalytic activity. This work proves that adding gallium oxides to palladium-based electrocatalysts increases electrical conductivity and causes the uniform dispersion of palladium nanoparticles on reduced graphene oxide surface.

Supercritical CO2 Mediated Multi‐scale Structural Engineering in PdCu/C for Boosting Electrocatalytic Formic Acid Oxidation

AbstractNowadays, PdCu alloy nanocatalyst with excellent performance in electrocatalytic formic acid oxidation reaction (FAOR) is believed to have great potential in application of direct formic acid fuel cells. Structural engineering has shown great success in achieving PdCu alloys with high catalytic performance, while achievement of multi‐scale structure engineering is still a great challenge. In this work, we found that supercritical carbon dioxide (SC CO2) could lead to multi‐scale structure engineering in PdCu/C nanocatalysts, including surface defect engineering, phase engineering, morphology engineering and substrate structure engineering. With the assistance of SC CO2, amorphous phase in surface, the transformation from face‐centered cubic (FCC) to body‐centered cubic (BCC) phase, the morphology of 2D nanoflakes and the curved carbon as substrate all contribute to the ultrahigh mass activity for electrocatalytic FAOR as 3624.3 mA/mgPd in PdCu/C nanocatalysts, which is the highest value in PdCu alloy reported up to now. Therefore, this work not only displays the great potential of SC CO2 in multi‐scale structure engineering, but also provides new inspiration of material design to achieve nanocatalysts with ultrahigh catalytic performance.

Boosting Electrocatalytic Oxidation of Formic Acid on Ir(IV)-Doped PdAg Alloy Nanodendrites with Sub-5 nm Branches.

The formic acid oxidation reaction (FAOR) represents an important class of small organic molecule oxidation and is central to the practical application of fuel cells. In this study, we report the fabrication of Ir(IV)-doped PdAg alloy nanodendrites with sub-5 nm branches via stepwise synthesis in which the precursors of Pd and Ag were co-reduced, followed by the addition of IrCl3 to conduct an in situ galvanic replacement reaction. When serving as the electrocatalyst for the FAOR in an acidic medium, Ir(IV) doping unambiguously enhanced the activity of PdAg alloy nanodendrites and improved the reaction kinetics and long-term stability. In particular, the carbon-supported PdAgIr nanodendrites exhibited a prominent mass activity with a value of 1.09 A mgPd-1, which is almost 2.0 times and 2.7 times that of their PdAg and Pd counterparts, and far superior to that of commercial Pt/C. As confirmed by the means of the DFT simulations, this improved electrocatalytic performance stems from the reduced overall barrier in the oxidation of formic acid into CO2 during the FAOR and successful d-band tuning, together with the stabilization of Pd atoms. The current study opens a new avenue for engineering Pd-based trimetallic nanocrystals with versatile control over the morphology and composition, shedding light on the design of advanced fuel cell electrocatalysts.

CeO2 promotes electrocatalytic formic acid oxidation of Pd-based alloys

Engineering metal/oxide interface and controlling composition are the important strategies that aim towards obtaining efficient Pd-based electrocatalysts (ECs). Rationally designed ECs for dehydrogenation of formic acid play a dynamic role in the proper utilization of its chemical energy. Herein, we report Pd3M alloy nanoparticles anchored on CCeO2 (Pd3M/CCeO2, M = Cu, Ni, Co) which shows significant performance towards formic acid oxidation (FAO). Interestingly, Pd3M/CCeO2 (M = Cu, Ni, Co) ECs displayed the best FAO activity via the “dehydrogenation” pathway. The remarkable performance can be mainly attributed to the proper electronic and synergistic effects between Pd and the alloyed metal, which leads to Pd lattice contraction and downshift of d-band center. It was also observed that the FAO activity of Pd3Cu/CCeO2 is superior to that of Pd3Co/CCeO2 and Pd3Ni/CCeO2. The oxygen vacancies in CeO2 and strong Pd/CeO2 interactions established by computational and experimental studies contribute towards the overall electrocatalytic behaviour.

A “Special” Solvent to Prepare Alloyed Pd2Ni1 Nanoclusters on a MWCNT Catalyst for Enhanced Electrocatalytic Oxidation of Formic Acid

Herein, an electrocatalyst with Pd2Ni1 nanoclusters, supporting multiwalled carbon nanotubes (MWCNTs) (referred to Pd2Ni1/CNTs), was fabricated with deep eutectic solvents (DES), which simultaneously served as reducing agent, dispersant, and solvent. The mass activity of the catalyst for formic acid oxidation reaction (FAOR) was increased nearly four times compared to a Pd/C catalyst. The excellent catalytic activity of Pd2Ni1/CNTs was ascribed to the special nanocluster structure and appropriate Ni doping, which changed the electron configuration of Pd to reduce the d-band and to produce a Pd-Ni bond as a new active sites. These newly added Ni sites obtained more OH- to release more effective active sites by interacting with the intermediate produced in the first step of FAOR. Hence, this study provides a new method for preparing a Pd-Ni catalyst with high catalytic performance.

Microwave-assisted synthesis of octahedral Rh nanocrystals and their performance for electrocatalytic oxidation of formic acid.

Uniform and well-defined octahedral Rh nanocrystals were rapidly synthesized in a domestic microwave oven for only 140 s of irradiation by reducing Rh(acac)3 with tetraethylene glycol (TEG) as both a solvent and a reducing agent in the presence of an appropriate amount of KI, didecyl dimethyl ammonium chloride (DDAC), ethylene diamine (EDA) and polyvinylpyrrolidone (PVP). KI, DDAC and EDA were essential for the creation of octahedral Rh nanocrystals. Electrochemical measurements showed a significantly enhanced electrocatalytic activity and stability for the as-prepared octahedral Rh nanocrystals compared with commercial Rh black.

Au(111) Surface Oxidation Kinetics Probed by Electrocatalytic Oxidation of Formic Acid

The kinetics of surface oxidation for Au(111) in 0.1 M HCOOH + 0.1 M HClO4 was studied at 20 °C utilizing the electrocatalytic formic acid oxidation reaction (FAOR). In the surface oxidation region, cyclic voltammetry shows a distinct dependence of FAOR on scan rate revealing simultaneous deactivation of active surface sites. The surface oxide is essentially inactive for the FAOR. A series of current-time curves was recorded after potential steps into the potential range between 0.65 and 1.00 V vs saturated Mercury-mercurous sulfate electrode and analyzed within a three-step surface oxidation model, which successively involves (i) adsorption at surface defects, (ii) adsorption on well-defined Au(111) terraces, and (iii) two-dimensional nucleation-and-growth on terraces. Although Au surface oxidation is by far more complex, the system can be described in terms of the intrinsic activity of the Au(111) surface and the oxide coverage The chronoamperometric measurements can be modeled without considering the interaction of the oxide species with the FAOR and the co-adsorption of anions. The potential dependence of the kinetic parameters is used to obtain theoretical current-time curves for FAOR on Au(111). This study sheds light on the “fast FAOR” and contributes to the understanding of degradation phenomena in electrocatalysis.

Electrochemical formic acid oxidation catalyzed by graphene supported bimetallic Pd-Ni clusters: The role of Ni content and the hydrogen coverage effect

By means of periodic density functional theory calculations, we have investigated the electrocatalytic formic acid oxidation (FAO) on graphene supported Pd-Ni catalysts and elucidate the detail about the role of Ni content in different Pd-Ni atomic ratio and the hydrogen coverage effect. The FAO reaction often onsets at low oxidation potential range, where deposition of hydrogen is alive and affect the catalytic performance of Pd-Ni clusters, accordingly, the FAO reaction on varied H* ratio Pd-Ni clusters accompanying with enhanced external potential is also considered. In our calculation, the H* saturated situation would suppress the formation of COOH* much more than that of HCOO*, even controlling the reaction energy of HCOO* from HCOOH become moderate in FAO reaction. In addition, the potential requirements to proceed the FAO reaction on Pd10-gra and Pd8Ni2-graphene are similar but Ni content could also suppress formation of COOH* and enhance the interaction between Pd8Ni2-graphene and HCOO* species. Pd6Ni4-grahene model is another choice for FAO reaction, in which the HCOO* species on clean Pd6Ni4-graphene model has lowest onset potential of 0.18 V for HCOO* deprotonation to CO2 in all of our models. However, excess Ni content would cause Ni exposed on Pd2Ni8-grahene, where the HCOO* is downhill in energy with a larger onset potential of 0.59 V for the deprotonation of HCOO*, but the hydride formation of 8H* and 9H* Pd2Ni8-graphene could overcome the question.

Boosting the anti-poisoning ability of palladium towards electrocatalytic formic acid oxidation via polyphosphide chemistry

In this work, we reported a novel polyphosphide strategy for the synthesis of phosphorus doped Pd (P-Pd) using red phosphorus as the starting material at quasi-ambient conditions. Polyphophide anions, as the key reaction intermediates, served as the reducing agent and phosphorus source to modulate the surface electronic structure of Pd. The P-Pd obtained exhibited topmost CO tolerance and electrocatalytic activity to formic acid oxidation among the state-of-arts reports. The mass activity and turnover frequency of P-Pd reached 4413 mA mg−1Pd and 16.04 s−1 at 0.8 V, which were 23.7 and 6.4 times that of commercial Pd/C respectively. After 1000 repeated cycles, 82% initial activity was reserved. Combined with the electrochemical analysis and the density functional theory calculation, the boosted electrochemical performances can be attributed to the size and electronic effects induced by the P doping, which increase the surface actives sites, inhibit the adsorption of CO and change the reaction pathway to favorable CO2 route. A full cell was also assembled to demonstrate the practical potential of the P-Pd, which showed a maximum power density of 21.56 mW cm−2. This polyphophide-based reaction route provides a new strategy for the preparation of efficient and durable phosphorus doped alloys for electrocatalysis.

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

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

How palladium inhibits CO poisoning during electrocatalytic formic acid oxidation and carbon dioxide reduction

Development of reversible and stable catalysts for the electrochemical reduction of CO2 is of great interest. Here, we elucidate the atomistic details of how a palladium electrocatalyst inhibits CO poisoning during both formic acid oxidation to carbon dioxide and carbon dioxide reduction to formic acid. We compare results obtained with a platinum single-crystal electrode modified with and without a single monolayer of palladium. We combine (high-scan-rate) cyclic voltammetry with density functional theory to explain the absence of CO poisoning on the palladium-modified electrode. We show how the high formate coverage on the palladium-modified electrode protects the surface from poisoning during formic acid oxidation, and how the adsorption of CO precursor dictates the delayed poisoning during CO2 reduction. The nature of the hydrogen adsorbed on the palladium-modified electrode is considerably different from platinum, supporting a model to explain the reversibility of this reaction. Our results help in designing catalysts for which CO poisoning needs to be avoided.

Achieving a Record High Activity of 8.08 a Mg-1pd for Electrocatalytic Formic Acid Oxidation Reaction Through P-Pdauag Quaternary Alloying

Achieving a Record High Activity of 8.08 a Mg-1pd for Electrocatalytic Formic Acid Oxidation Reaction Through P-Pdauag Quaternary Alloying

Enhanced electrocatalytic activity of Cu-modified, high-index single Pt NPs for formic acid oxidation.

A key goal of nanoparticle-based catalysis research is to correlate the structure of nanoparticles (NPs) to their catalytic function. The most common approach for achieving this goal is to synthesize ensembles of NPs, characterize the ensemble, and then evaluate its catalytic properties. This approach is effective, but it excludes the certainty of structural heterogeneity in the NP ensemble. One means of addressing this shortcoming is to carry out analyses on individual NPs. This approach makes it possible to establish direct correlations between structures of single NPs and, in the case reported here, their electrocatalytic properties. Accordingly, we report on enhanced electrocatalytic formic acid oxidation (FAO) activity using individual Cu-modified, high-indexed Pt NPs. The results show that the Cu-modified Pt NPs exhibit significantly higher currents for FAO than the Pt-only analogs. The increased activity is enabled by the Cu submonolayer on the highly stepped Pt surface, which enhances the direct FAO pathway but not the indirect pathway which proceeds via surface-absorbed CO*.

Fabrication of GC-r-GO-PAMAM (G3)-Pd electrode for electro-catalytic oxidation of formic acid

Graphene functionalized with Poly(amidoamine) dendrimer stabilized PdNPs (r-GO-PAMAM-Pd) composite was prepared through facile experimental routes and characterized by FT-IR, XRD, Raman, SEM and EDAX techniques. Initially, poly(amidoamine) generation 3 (PAMAM (G3)) dendrimer was functionalized on graphene oxide (GO) and the resulting matrix was loaded with PdNPs through stabilization and thus produced excellent conducting composite material. The electro-catalytic activity of this composite was inspected by coating on bare GCE and thus produced stable and efficient GC-r-GO-PAMAM (G3)-Pd electrode and this in turn demonstrated for the oxidation of formic acid (FA). The occurrence of the oxidation reaction was monitored by cyclic voltammetric (CV) and linear sweep voltammetric (LSV) techniques in 0.5 M H2SO4 medium at the potential window of -0.3 to 1.0 V vs. Ag/AgCl, v = 50 mVs-1. The observed peak potential for the new electrode was located at 0.15V and compared with existing electrodes derived from different GO/Pd composites.The comparative results reveals that the newly designed electrode shown an excellent catalytic activity, more resistant to the surface poisoning and the anodic onset potential was more negative than the reported electrodes. This improved electro-catalytic performance are due to the contribution of synergetic effect of GO, dendrimer and PdNPs. Copyright © 2018 VBRI Press.

Ligand‐Mediated Self‐Terminating Growth of Single‐Atom Pt on Au Nanocrystals for Improved Formic Acid Oxidation Activity

AbstractDecreasing the ensemble size of Pt to isolated single atoms is the key to enhance the electrocatalytic formic acid oxidation reaction (FAOR) by bypassing the indirect reaction path that involves the poisoning by the CO intermediate. However, it is challenging to construct isolated Pt single atoms on a foreign metal substrate, especially at high Pt loadings, because Pt tends to form large ensembles due to the high Pt–Pt bond energy. Herein, a ligand‐mediated self‐terminating growth strategy is reported for reliably controlling the ensemble size of Pt on an Au substrate. The key is to introduce a ligand of sulfite (SO32−) into the synthesis, which preferentially adsorbs at Pt sites, thus substantially increasing the kinetic barrier toward Pt–Pt bond formation. This strategy enables reliable formation of isolated Pt single atoms even at high Pt loadings (up to 26% coverage on Au), which is difficult to achieve by regular syntheses. The resulting catalyst exhibits a high FAOR activity of 38.6 A mgPt−1 in 0.5 m H2SO4+0.25 m HCOOH, 370 times greater than that of the commercial Pt/C. It is believed this strategy is general and potentially applicable to the fabrication of a wide range of noble metal catalysts with tailored ensemble sizes for energy conversion.

Electrocatalytic oxidation of formic acid by palladium nanoparticles electrochemically synthesized from a deep eutectic solvent

Palladium nanoparticles (PdNPs) were formed and supported onto the surface of a glassy carbon electrode (GCE) from a single potentiostatic step using palladium chloride (PdCl2) as the precursor salt, dissolved in a deep eutectic mixture formed by 2-Hydroxy-N,N,N-trimethylethanaminium chloride (choline chloride) and diaminomethanal (urea). Analysis of the potentiostatic current density transients allows to accurately establish the amount of Pd deposited on the GCE surface required to determine the so-called mass activity, as defined by the ratio between methanoic acid (formic acid) oxidation current and palladium mass electrodeposited on the electrode. From SEM analysis of the GCE surface modified with PdNPs, it was found that PdNPs were distributed uniformly over the electrode surface, having an average size of (60 ± 9) nm. EDX and XPS analysis confirm a core-shell morphology constituted by a Pd core surrounded by a palladium (II) Hydroxide- palladium (II) oxide (Pd(OH)2-PdO) shell. The GCE modified with PdNPs (GCE/PdNPs) were used to oxidize formic acid from aqueous electrolytic baths added with perchloric acid (HClO4) or sulfuric acid (H2SO4). It was shown that the maximum mass activity depended on both, the nature of the electrolytic bath and the applied potential for the PdNPs electrodeposition. However, the best mass activity ((5085 ± 129) mA mgPd−1) was achieved with the GCE/PdNPs, formed at −700 mV vs. the silver quasi reference electrode (Ag QRE), immersed in the HClO4 electrolytic bath, even when the formic acid concentration was half that used in the H2SO4 electrolytic bath. Furthermore, the mass activities of the PdNPs reported in this work rank high among other values reported in the literature for nanoparticles based on palladium but synthesized with more complex and expensive processes, having the advantage of being obtained by a simple, rapid, and cost-effective electrochemical method.

Boosting electrocatalytic oxidation of formic acid on SnO2-decorated Pd nanosheets

Formic acid (HCOOH), as a natural biomass, is a promising feedstock for low temperature fuel cells, and rational development of efficient catalysts for electrochemical dehydrogenation of HCOOH plays a key role toward its full chemical energy utilization. Herein, Pd nanosheets decorated with SnO2 nanoflakes (denoted hereafter as Pd@SnO2-NSs) are designed as a composite catalyst, showing superior performance for formic acid electro-oxidation, as compared to pristine Pd nanosheets (Pd-NSs). In situ attenuated total reflection infrared (ATR-IR) spectroscopic results suggest a promoted formate pathway on the Pd@SnO2-NSs with a suppressed accumulation of CO poisoning species. DFT calculations further indicate that the Pd (111) surface modified with SnO2 has lower energy barriers for the bidentate formate formation, the bidentate to monodentate formate transformation and the C-H bond scission.

Adsorbed Formate is the Last Common Intermediate in the Dual-Path Mechanism of the Electrooxidation of Formic Acid

We report a study using Pt(111) and Pt(100) electrodes of the role of adsorbed formate in both the direct and indirect pathways of the electrocatalytic oxidation of formic acid. Cyclic voltammetry ...

Boosted electrocatalytic oxidation of formic acid at CoOx/Pd/Au nanoparticle-based ternary catalyst

Tailoring and designing of an efficient catalyst for the direct formic acid fuel cell industry is very imperative. Herein, various Pd-based electrocatalysts for formic acid electro-oxidation (FAO) are introduced. The ternary CoOx/Pd/Au catalyst, in which Au nanoparticles (nano-Au), Pd nanoparticles (nano-Pd) and cobalt oxide nanoparticles (nano-CoOx) are, sequentially, electrodeposited onto a glassy carbon (GC) substrate offering a boosted catalysis towards formic acid electro-oxidation (FAO). This study reveals that the electrocatalytic activity of the catalyst toward FAO depends on the catalyst's composition, loading level, and sequence of deposition. FE-SEM, EDS, and XRD are used to determine the surface morphology, composition, and crystallographic orientation, respectively. Cyclic voltammetry is employed to probe the electrochemical surface area (ECSA) of the various electrodes and to probe their activity. Compared to Pd/GC, Au/Pd/GC and Pd/Au/GC catalysts, the ternary CoOx/Pd/Au/GC catalyst features a higher oxidation peak current for FAO, Ip (ca. Eightfold), a better reversibility ratio, Ipf/Ipb (≅ 1), and a significant negative shift in the onset potential, Eonset (ca. 70 mV) of FAO together with a higher stability of FAO current. Capacitance (Cre-Cim) measurements reveal the superiority of the ternary catalyst over the other catalysts in terms of higher capacitance which is in line with the order of the observed catalytic activity. That is the capacitance of CoOx/Pd/Au/GC electrode/electrolyte interface is ten times higher than that of Pd/GC electrode.

Synthesis of ultrafine low loading Pd–Cu alloy catalysts supported on graphene with excellent electrocatalytic performance for formic acid oxidation

Here, surfactant free composite catalysts (Pd–Cu/rGO) with Pd–Cu alloy nanoparticles uniformly distributed on graphene sheets are successfully prepared via a facile hydrothermal approach. Compared with pure Pd/rGO catalyst, the introduction of copper could dramatically enhance the performance of the catalyst in the electrocatalytic formic acid oxidation (FAO) due to the strain effect and the ligand effect. With the optimized atomic ratio of 3:1 between palladium and copper, the alloy nanoparticle shows the smallest size of 2.12 nm, thus endowing the composite catalyst with highest catalytic efficiency. With Pd load as low as 14.5%, a maximum mass current density of 1580 mA mgPd−1, and residual current of 69.93 mA mgPd−1 at 3000 s was achieved with our Pd3Cu1/rGO catalyst in the electrocatalytic FAO process.