Formic Acid Electrooxidation Reaction Research Articles

Synergistic effects of NiPtCo/Ti0.7W0.3O2 hybrid electrocatalysts for accelerating formic acid electro-oxidation performance.

We herein report the fabrication strategy of a robust catalyst for the formic acid electro-oxidation reaction (FAOR) via combining the advantages of a TiO2-related support and the synergistic effects of NiPtCo alloy. With the predominant dehydrogenation pathway, the NiPtCo/Ti0.7W0.3O2 catalyst shows remarkable FAOR mass activity and specific activity of 0.45 A mgMetal-1 and 1.25 mA cm-2, being 3.75- and 4.81-time higher than those of the commercially available Pt/C, respectively. The as-made FAOR electrocatalyst shows superior CO-tolerance and electrocatalytic stability during long-term operation conditions due to the synergistic contributions of each component in the overall catalyst system.

Palladium‐Boride Nanoflowers with Controllable Boron Content for Formic Acid Electrooxidation

AbstractThe rational design of the electronic structure and elemental compositions of anode electrocatalysts for formic acid electrooxidation reaction (FAOR) is paramount for realizing high‐performance direct formic acid fuel cells. Herein, palladium‐boride nanoflowers (Pd‐B NFs) with controllable boron content are rationally designed via a simple wet chemical reduction method, utilizing PdII‐dimethylglyoxime as precursor and NaBH4 as both reductant and boron source. The boron content of Pd‐B NFs can be regulated through manipulation of reaction time, accompanying with the crystal phase transition from face‐centered cubic to hexagonal close‐packed within the parent Pd lattice. The obtained Pd‐B NFs exhibit increased FAOR mass and specific activity with increasing boron content, showcasing remarkable inherent stability and anti‐poisoning capability compare to commercial Pd and platinum (Pt) nanocrystals. Notably, the sample reacted for 12 h reveals high FAOR specific activity (31.5 A m−2), which is approximately two times higher than the commercial Pd nanocrystals. Density functional theory calculations disclose that the d‐sp orbital hybridization between Pd and B modifies surface d‐band properties of Pd, thereby optimizing the adsorption of key intermediates and facilitating FAOR kinetics on the Pd surface. This study paves the way toward the utilization of metal boride‐based materials with simple synthesis methods for various electrocatalysis applications.

Influence of TiO2 coverage on activity and stability of Pd-TiO2/MWCNT-supported catalysts used in direct formic acid fuel cells

Pd and TiO2 supported on functionalized multiwall carbon nanotubes (f-MWCNTs) catalysts were investigated in formic acid electrooxidation reaction in direct formic acid fuel cell. TiO2 (5–60 wt.% loading) on f-MWCNTs was deposited using microwave-assisted hydrothermal method. 20 wt.% of Pd was deposited on TiO2/f-MWCNTs by reduction of palladium (II) chloride salt with sodium borohydride. Catalysts’ structure and composition were characterized by XRD, STEM, HR-TEM, TGA, XPS/XAES (Pd, Ti, O spectra features, density of valence states, Auger parameters). Average crystallite size of Pd and TiO2 from XRD (3–4 nm) agrees with those by HR-TEM (3–5 nm). Low TiO2 coverages (below 32wt.%) show smaller crystallites due to increased surface hydrophilicity, higher amount of TiO2 oxygen vacancies with attached Pd nanoparticles, increased density of valence states of strong Pd–TiO2 interface. In contrary, the higher coverages indicate lower amount of Pd–O–Ti, Ti–O–C, Pd–O–C interfaces, with electron charge transfer from TiO2 to f-MWCNTs, and to Pd. Catalysts activity (40–106 mWmgPd−1) and stability (5–240 h) are enhanced at low TiO2 coverages (4–8 wt.%) due to a strong Pd-TiO2 interface on oxygen vacancies, improved electron transport and a high active surface area. Oscillatory self-cleaning mechanism of Pd is due to oxidation by -OH groups (TiO2, f-MWCNTs), and hydrogen and CO spillover.

Enhanced formic acid electro-oxidation reaction over Ir,N-doped TiO2-supported Pt nanocatalyst

In this work, we prepared an Ir,N-doped TiO2 nanomaterial via a facile HNO3-assisted hydrothermal process that was used as an advanced support for nano-sized Pt nanoparticles (NPs) for the formic acid oxidation reaction (FAOR). The physical and electrochemical behaviours of the as-made Pt/Ir,N-doped TiO2 catalyst were systemically investigated through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopes coupled with energy dispersive X-ray analysis (FE-SEM/EDX mapping), transmission electron microscopy (TEM), linear sweep voltammetry (LSV), Tafel slope, CO-stripping, and chronoamperometric (CA) test. The Pt NPs (ca. 3 nm) were anchored on the Ir,N-doped TiO2 support, being formed by a mixture of rutile and brookite with a particle size of several ten nanometers. Due to the small size and uniform distribution of Pt NPs, the Pt/Ir,N-doped TiO2 catalyst had an electrochemical surface area of 79.88 m2 g−1, which was greater than that of the commercial Pt/C (77.63 m2 g−1). In terms of the FAOR, the Pt/Ir,N-doped TiO2 catalyst showed a negative FAOR onset potential, high current density (11.85 mA cm−2), and superior CO-tolerance compared to the commercially available catalyst. Also, the as-made catalyst possessed high electrochemical durability after 3600 s for testing. The enhanced FAOR efficiency was assigned to the formation of a dual-doping effect and strong interplay between Pt and TiO2-based support, which not only improved the electron transfer but also weakened the adsorption of carbonaceous species, thereby boosting the reaction kinetics. This study could open up a facile but effective strategy to promote particular electrochemical applications.

In-situ Bi-modified Pt towards glycerol and formic acid electro-oxidation: Effects of catalyst structure and surface microenvironment on activity and selectivity

The performances of glycerol electro-oxidation reaction (GOR) and formic acid electro-oxidation reaction (FAOR) catalyzed by Pt catalyst were dramatically improved by adding Bi3+ into the reaction solution. The dynamic structure and microenvironment of in-situ Bi-modified Pt and their impact on the catalytic performances were revealed. A strong correlation was established between the Bi coverage of Pt-based catalysts and their resistance to CO poisoning and performance in GOR and FAOR. When Bi3+ increased to a certain amount, a Bi-shell containing hydroxides was formed on Pt surfaces except the formation of Pt-Bi ensemble. On Pt catalyst covered with 43.9 % Bi, the peak mass-specific activities of GOR and FAOR in forward scans were 4.2 and 34.7 times that of Pt/NCNTs, respectively. The peak electrochemical active surface area (ECSA)-specific activity of FAOR in forward scan for Pt with 52.6 % Bi coverage was 80.6 times that of Pt/NCNTs. The dehydrogenation process in FAOR and the 4-electron pathway in GOR were improved for Bi-modified Pt. The experimental results and DFT calculations indicated that the positively charged Bi and structure of Pt-Bi ensemble improved the adsorption and interaction of negatively charged intermediates, and the enhanced hydroxides facilitated the oxidation and removal of toxic intermediates, such as CO.

Chemical functionalization of commercial Pt/C electrocatalyst towards formic acid electrooxidation

The chemical functionalization on the noble metal surface will undoubtedly affect the electrode reaction process. In this work, 1,10-phenanthroline (PL) functionalized commercial Pt/C electrocatalyst (Pt/C@PL) is successfully achieved through a convenient post-modification strategy. The adsorption of PL molecules on Pt/C electrocatalyst surface effectively isolates the continuous Pt atoms. Consequently, the formic acid electrooxidation reaction (FAOR) on Pt/C@PL electrocatalyst only obeys the dehydrogenation pathway, in which the generation of COads is completely suppressed. Compared with unfunctionalized commercial Pt/C electrocatalyst, Pt/C@PL electrocatalyst reveals a 11.4/16.8-fold increase in mass/specific activity, exhibiting a prominently enhanced electrocatalytic performance towards FAOR. This strategy, the chemical functionalization on the electrocatalysts surface, is easy to operate and applicable to commercial electrocatalyst that already exist, which also provides a simple and efficient way in the design of advanced electrocatalysts towards many other electrochemical reactions.

Synthesis of new Pd@NDG electrocatalyst by using g-C3N4/GO hydrogel toward formic acid electrooxidation reaction in direct formic acid fuel cell

In this research, the new Pd@NDG electrocatalyst was evaluated for the formic acid oxidation reaction. The nitrogen-doped graphene nanosheets (NDG) support was obtained by heating the g-C3N4/GO hydrogel in an inert atmosphere. The Pd@NDG electrocatalyst was prepared by combined use of NDG and palladium chloride via a one-stage reduction using ascorbic acid. The as-prepared Pd@NDG electrocatalyst displayed high catalytic activity in formic acid oxidation. The significant electrocatalytic performance stems from the presence of the NDG support in the structure of the electrocatalyst. The NDG support improved the physicochemical properties of the catalyst. The NDG support acts as an excellent ligand and leads to increase dispersion of Pd. The number of active metal sites is enhanced by increasing dispersion and exposing the surface area of the electrocatalyst and improving electronic properties, which lead to improving the catalytic performance of the catalyst. Furthermore, the formic acid electrocatalytic activity and the durability of Pd@NDG electrocatalyst as compared to the Pd/C commercial benchmark catalyst. The results displayed that the Pd@NDG electrocatalyst has better performance for formic acid oxidation.

Focused microwave-assisted synthesis of activated XC-72R supported PdBi nanocatalyst for the enhanced electrocatalytic performance in formic acid oxidation

The present paper describes a rapid and straightforward synthesis technique called focused microwave-assisted synthesis (FMWS) for producing bimetallic carbon-based PdBi@C nanocomposites with desired monodispersity and uniformity and investigates their catalytic activity towards formic acid electro-oxidation reaction (FAOR). X-ray diffraction (XRD), transmission electron microscope (TEM), and energy dispersive X-ray (EDX) analysis confirmed that Pd atoms are embedded in the activated XC-72 R carbon support, and the resulting Pd@C surface shows excellent integration with Bi atoms via spontaneous chemisorption after FMWS. The synthesized Pd20Bi1@C nanocatalyst displayed optimal electrochemical performance for direct formic acid oxidation reaction (DFAOR), with uniform dispersity, a narrow size distribution (6.54 ± 1.03 nm), and a polydispersity index (PDI) of 16%, indicating high monodispersity achieved through FMWS. The influence of nanocomposite content on DFAOR was investigated, revealing that Pd20Bi1@C exhibited a significantly higher current density compared to salt Pd@C, with a 2.63-fold increase. The evaluated nanocatalysts ranked in descending order of final current densities (mAcm−2) as follows: Pd20Bi1@C (21.06) > Pd30Bi1@C (14.31) > Pd40Bi1@C (12.09) > Pd10Bi1@C (9.22) > Pd@C (8.02). Furthermore, chronoamperometry and cyclic voltammetry tests demonstrated that the addition of Bi to Pd@C enhanced the reaction of oxygenated species with CO-like poisonous intermediates, thereby facilitating the adsorption and oxidation of formic acid molecules by releasing Pd active sites in DFAOR. Notably, Pd20Bi1@C exhibited exceptional stability and improved CO tolerance. In summary, the current study highlights the potential of integrating FMWS with a chemisorption approach to achieve excellent electrochemical performance, enabling nanocomposites to demonstrate enhanced feasibility as prospective catalysts for FAOR.

Pt-Te alloy nanowires towards formic acid electrooxidation reaction

The high-performance anodic electrocatalysts is pivotal for realizing the commercial application of the direct formic acid fuel cells. In this work, a simple polyethyleneimine-assisted galvanic replacement reaction is applied to synthesize the high-quality PtTe alloy nanowires (PtTe NW) by using Te NW as an efficient sacrificial template. The existence of Te atoms separates the continuous Pt atoms, triggering a direct reaction pathway of formic acid electrooxidation reaction (FAEOR) at PtTe NW. The one-dimensional architecture and highly active sites have enabled PtTe NW to reveal outstanding electrocatalytic activity towards FAEOR with the mass/specific activities of 1091.25 mA mg−1/45.34 A m−2 at 0.643 V potential, which are 44.72/23.16 and 20.26/11.75 times bigger than those of the commercial Pt and Pd nanoparticles, respectively. Density functional theory calculations reveal that Te atoms optimize the electronic structure of Pt atoms, which decreases the adsorption capacity of CO intermediate and simultaneously improves the durability of PtTe NW towards FAEOR. This work provides the valuable insights into the synthesis and design of efficient Pt-based alloy FAEOR electrocatalysts.

Co-electrodeposited PtPd anodic catalyst for the direct formic acid fuel cells

This investigation displayed a superb catalytic performance toward the formic acid electro-oxidation reaction (FAOR) in an alkaline medium at a binary catalyst composed of Pt and Pd that were simultaneously electrodeposited onto a glassy carbon (GC) surface. Interestingly, the proposed PtPd/GC catalyst displayed a significant enhancement in the catalytic activity (by ca. 12 times higher direct (Ipd) to indirect (Ipind) current ratio concurrently with ca. -91 mV shift in the onset potential (Eonset) and stability (ca. 2.5 times higher current density after 3600 s of continuous electrolysis) toward FAOR if compared to the Pt/GC catalyst. The catalytic enhancement was thought to arise mostly from minimizing the CO adsorption, i.e., third body effect, at the Pt surface during FAOR.

Interfacial engineering of holey platinum nanotubes for formic acid electrooxidation boosted water splitting

Both structure and interface engineering are highly effective strategies for enhancing the catalytic activity and selectivity of precious metal nanostructures. In this work, we develop a facile pyrolysis strategy to synthesize the high-quality holey platinum nanotubes (Pt-H-NTs) using nanorods-like PtII-phenanthroline (PT) coordination compound as self-template and self-reduction precursor. Then, an up-bottom strategy is used to further synthesize polyallylamine (PA) modified Pt-H-NTs (Pt-H-NTs@PA). PA modification sharply promotes the catalytic activity of Pt-H-NTs for the formic acid electrooxidation reaction (FAEOR) by the direct reaction pathway. Meanwhile, PA modification also elevates the catalytic activity of Pt-H-NTs for the hydrogen evolution reaction (HER) by the proton enrichment at electrolyte/electrode interface. Benefiting from the high catalytic activity of Pt-H-NTs@PA for both FAEOR and HER, a two-electrode FAEOR boosted water electrolysis system is fabricated by using Pt-H-NTs@PA as bifunctional electrocatalysts. Such FAEOR boosted water electrolysis system only requires the operational voltage of 0.47 V to achieve the high-purity hydrogen production, showing an energy-saving hydrogen production strategy compared to traditional water electrolysis system.

Determining the role of Pd catalyst morphology and deposition criteria over large area plasmonic metasurfaces during light-enhanced electrochemical oxidation of formic acid

The use of metal composites based on plasmonic nanostructures partnered with catalytic counterparts has recently emerged as a promising approach in the field of plasmon-enhanced electrocatalysis. Here, we report on the role of the surface morphology, size, and anchored site of Pd catalysts coupled to plasmonic metasurfaces formed by periodic arrays of multimetallic Ni/Au nanopillars for formic acid electro-oxidation reaction (FAOR). We compare the activity of two kinds of metasurfaces differing in the positioning of the catalytic Pd nanoparticles. In the first case, the Pd nanoparticles have a polyhedron crystal morphology with exposed (200) facets and were deposited over the Ni/Au metasurfaces in a site-selective fashion by limiting their growth at the electromagnetic hot spots (Ni/Au-Pd@W). In contrast, the second case consists of spherical Pd nanoparticles grown in solution, which are homogeneously deposited onto the Ni/Au metasurface (Ni/Au-Pd@M). Ni/Au-Pd@W catalytic metasurfaces demonstrated higher light-enhanced FAOR activity (61%) in comparison to the Ni/Au-Pd@M sample (42%) for the direct dehydrogenation pathway. Moreover, the site-selective Pd deposition promotes the growth of nanoparticles favoring a more selective catalytic behavior and a lower degree of CO poisoning on Pd surface. The use of cyclic voltammetry, energy-resolved incident photon to current conversion efficiency, open circuit potential, and electrochemical impedance spectroscopy highlights the role of plasmonic near fields and hot holes in driving the catalytic enhancement under light conditions.

Augmented formic acid electro-oxidation at a co-electrodeposited Pd/Au nanoparticle catalyst

In this study, the formic acid electro-oxidation reaction (FAEOR) was catalyzed on a Pd-Au co-electrodeposited binary catalyst. The kinetics of FAEOR were intensively impacted by changing the Pd2+:Au3+ molar ratio in the deposition medium. The Pd1-Au1 catalyst (for which the Pd2+:Au3+ molar ratio was 1:1) acquired the highest activity with a peak current density for the direct FAEOR (Ip) of 4.14 mA cm−2 (ca. 13- times higher than that (ca. 0.33 mA cm−2) of the pristine Pd1-Au0 catalyst). It also retained the highest stability that was denoted in fulfilling ca. 0.292 mA cm−2 (ca. 19-times higher than 0.015 mA cm−2 of the pristine Pd1-Au0 catalyst) after 3600 s of continuous electrolysis at 0.05 V. The CO stripping and impedance measurements confirmed, respectively, the geometrical and electronic enhancements in the proposed catalyst.

Tuning atomic Pt site surface on PtAu alloy toward electro-oxidation of formic acid

PtAu alloy is considered to be a promising catalyst for the formic acid (HCOOH) electro-oxidation reaction. Nevertheless, the mechanism of HCOOH electro-oxidation on various surface compositions of PtAu is still unclear. Here, a series of ∼5 nm PtAu catalysts from Pt50Au50 to atomically dispersed Pt surface is successfully prepared. We reveal that the electro-oxidation HCOOH mechanism depends on the surface Pt sites; i.e., when PtAu alloy surface tunes to surface atomic Pt site, their mechanisms will change from a dual pathway mechanism to a direct pathway. Therefore, PtAu alloy (Pt5Au95) with atomic Pt sites surface showed an excellent activity with 104.8 mA cm−2 at 0.24 V (normalized by the Pt active surface area), which is five times higher than that of Pt50Au50 (19.3 mA cm−2 at 0.24 V) toward HCOOH electro-oxidation. Significantly, external reflection in-situ Fourier transform infrared spectroscopy (FTIRS) results furtherly prove that the atomic Pt sites surface on PtAu alloy will prevent the formation of CO poisoning intermediate and undergo the direct pathway to form CO2. Moreover, attenuated total reflection (ATR) in-situ FTIRS results also demonstrate that the bridge formic acid anion on PtAu alloy is not a real intermediate for electro-oxidation HCOOH.

A new pathway for formic acid electro-oxidation: The electro-chemically decomposed hydrogen as a reaction intermediate

Formic acid electro-oxidation reaction (FAOR) is generally believed that follows a two-pathway mechanism. Herein, we resorted to in situ electrochemical mass spectrometry and successfully captured the trace of H2, as the new intermediate species, during the process of FAOR on both Pt based catalyst and two single atom catalysts (Rh-N-C and Ir-N-C). Inspired by this, we proposed a new reaction path named hydrogen oxidation pathway: at the oxidation potential, formic acid will break the C–H bond and combine with the protons in the solution to form H2 species, then hydrogen oxidation reaction (HOR) will occur to generate two protons. This process is accompanied by electron transfer and contributes currently to the whole reaction.

Steady State Kinetic Study of the Formic Acid Electrooxidation Reaction on Iridium in a Flow Cell

Steady State Kinetic Study of the Formic Acid Electrooxidation Reaction on Iridium in a Flow Cell

Synergistic enhancement of formic acid electro-oxidation on PtxCuy co-electrodeposited binary catalysts

A propitious binary catalyst composed of Pt and Cu which were electrodeposited simultaneously onto a glassy carbon (GC) substrate was recommended for the formic acid (FA) electro-oxidation reaction (FAOR); the principal anodic reaction in the direct FA fuel cells (DFAFCs). The simultaneous co-electrodeposition of Pt and Cu in the catalyst provided an opportunity to tune the geometric functionality of the catalyst to resist the adsorption of poisoning CO at the Pt surface that represented the major impediment for DFAFCs marketing. The catalytic activity of the catalyst toward FAOR was significantly influenced by the (Pt4+/Cu2+) molar ratio of the electrolyte during electrodeposition, which also affected the surface coverage of Pt and Cu in the catalyst. Interestingly, with a molar (Pt4+/Cu2+) ratio of (1:4), the catalyst sustained superior (3.58 compared to 0.65 obtained at the pristine Pt/GC catalyst) activity for FAOR, concurrently with up to four-times (0.73 compared to 0.18 obtained at the pristine Pt/GC catalyst) improvement in the catalytic tolerance against CO poisoning. This associated, surprisingly, a negative shift of ca. 336 mV in the onset potential of FAOR, in an indication for the competitiveness of the catalyst to minimize superfluous polarizations in DFAFCs. Furthermore, it offered a better (ended up with 20% loss in the activity) stability for continuous (1 h) electrolysis than pristine Pt/GC catalyst (the loss reached 35%). The impedance and CO stripping measurements together excluded the electronic element but confirmed the geometrical influence in the catalytic enhancement.

Tailor-designed nanowire-structured iron and nickel oxides on platinum catalyst for formic acid electro-oxidation.

This investigation is concerned with designing efficient catalysts for direct formic acid fuel cells. A ternary catalyst containing iron (nano-FeOx) and nickel (nano-NiOx) nanowire oxides assembled sequentially onto a bare platinum (bare-Pt) substrate was recommended for the formic acid electro-oxidation reaction (FAOR). While nano-NiOx appeared as fibrillar nanowire bundles (ca. 82 nm and 4.2 μm average diameter and length, respectively), nano-FeOx was deposited as intersecting nanowires (ca. 74 nm and 400 nm average diameter and length, respectively). The electrocatalytic activity of the catalyst toward the FAOR depended on its composition and loading sequence. The FeOx/NiOx/Pt catalyst exhibited ca. 4.8 and 1.6 times increases in the catalytic activity and tolerance against CO poisoning, respectively, during the FAOR, relative to the bare-Pt catalyst. Interestingly, with a simple activation of the FeOx/NiOx/Pt catalyst at −0.5 V vs. Ag/AgCl/KCl (sat.) in 0.2 mol L−1 NaOH, a favorable Fe2+/Fe3+ transformation succeeded in mitigating the permanent CO poisoning of the Pt-based catalysts. Interestingly, this activated a-FeOx/NiOx/Pt catalyst had an activity 7 times higher than that of bare-Pt with an ca. −122 mV shift in the onset potential of the FAOR. The presence of nano-FeOx and nano-NiOx enriched the catalyst surface with extra oxygen moieties that counteracted the CO poisoning of the Pt substrate and electronically facilitated the kinetics of the FAOR, as revealed from CO stripping and impedance spectra.

Engineering Ir Atomic Configuration for Switching the Pathway of Formic Acid Electrooxidation Reaction

AbstractSwitching the formic acid oxidation reaction (FAOR) pathway from CO intermediate to direct CO2 formation is essential for noble‐metal electrocatalysts, but rare investigations on Ir‐based materials. Herein, the atomic configurations of Ir are controlled to enhance the FAOR performance via Ir3V intermetallics (O‐Ir3V). As the ordering degree of O‐Ir3V increases, the Ir ensemble size decreases to trimer and dimer, leading to a 7.3 times promotion in mass normalized activity relative to Ir. Supported by electrochemical in situ attenuated total reflection infrared spectroscopy results, it shows that FAOR occurs via linear CO mediated pathway on Ir, but it is totally switched to a direct pathway on highly ordered O‐Ir3V. The preserved ordered structure and V oxides on the surface during the durability test contribute to the enhanced stability. This study provides an idea to switch the FAOR pathway through tuning the Ir atom configuration by constructing ordered intermetallics.

Formic acid electrooxidation on small, {1 0 0} structured, and Pd decorated carbon-supported Pt nanoparticles

The use of shape-controlled nanomaterials represents an elegant way to improve the performance of many electrochemical reactions. However, two main aspects must be still optimised: decreasing particle size and increasing their activity. This study shows that the deposition of Pd on different small (3–5 nm) supported Pt materials (displaying a preferential structure containing ~40% of Pt{100} terraces) leads to a great enhancement in the electrocatalytic activity towards the formic acid electrooxidation reaction. After Pd decoration, the oxidation takes place at lower overpotentials and oxidation current densities are significantly higher than those observed with all the bare Pt/C samples. For the Pt/C 45% catalyst, the intrinsic activity after Pd deposition was more than three times of that without Pd, while the oxidation overpotential shifted about ~200 mV to lower overpotentials.