Formic Acid Electrooxidation Research Articles

A hybrid FeOx/CoOx/Pt ternary nanocatalyst for augmented catalysis of formic acid electro-oxidation

Platinum-based catalysts that have long been used as the anodes for the formic acid electro-oxidation (FAO) in the direct formic acid fuel cells (DFAFCs) were susceptible to retrogradation in performance due to CO poisoning that impaired the technology transfer in industry. This work is designed to overcome this challenge by amending the Pt surface sequentially with nanosized cobalt (nano-CoOx, fibril texture of ca. 200 nm in particle size) and iron (nano-FeOx, nanorods of particle size and length of 80 and 253 nm, respectively) oxides. This enriched the Pt surface with oxygenated groups that boosted FAO and mitigated the CO poisoning. The unfilled d-orbitals of the transition metals and their tendency to vary their oxidations states presumed their participation in a faster mechanism of FAO. Engineering the Pt surface in this FeOx/CoOx/Pt hierarchy resulted in a remarkable activity toward FAO, that exceeded four times that of the Pt catalyst with up to ca. 2.5 times improvement in the catalytic tolerance against CO poisoning. This associated a ca. − 32 mV shift in the onset potential of FAO which increased to − 40 mV with a post-activation of the same catalyst at − 0.5 in 0.2 mol L–1 NaOH, displaying the catalyst's competitiveness in reducing overpotentials in DFAFCs. It also exhibited a favorable amelioration in the catalytic durability in long-termed chronoamperometric electrolysis. The electrochemical impedance spectroscopy and the CO stripping voltammetry were employed to elucidate the origin of enhancement.

PtPdAg nanotrees with low Pt content for high CO tolerance within formic acid and methanol electrooxidation

PtPdAg nanotrees with low Pt content for high CO tolerance within formic acid and methanol electrooxidation

PtPd catalysts dispersed on coal-based nitrogen-doped carbon nanotubes for formic acid electro-oxidation

PtPd catalysts dispersed on coal-based nitrogen-doped carbon nanotubes for formic acid electro-oxidation

Ultra-Large Two-Dimensional Metal Nanowire Networks by Microfluidic Laminar Flow Synthesis for Formic Acid Electrooxidation.

Despite the great research interest in two-dimensional metal nanowire networks (2D MNWNs) due to their large specific surface area and abundance of unsaturated coordination atoms, their controllable synthesis still remains a significant challenge. Herein, a microfluidics laminar flow-based approach is developed, enabling the facile preparation of large-scale 2D structures with diverse alloy compositions, such as PtBi, AuBi, PdBi, PtPdBi, and PtAuCu alloys. Remarkably, these 2D MNWNs can reach sizes up to submillimeter scale (~220 μm), which is significantly larger than the evolution from the 1D or 3D counterparts that typically measure only tens of nanometers. The PdBi 2D MNWNs affords the highest specific activity for formic acid (2669.1 mA mg-1) among current unsupported catalysts, which is 103.5 times higher than Pt-black, respectively. Furthermore, in situ Fourier transform infrared (FTIR) experiments provide comprehensive evidence that PdBi 2D MNWNs catalysts can effectively prevent CO* poisoning, resulting in exceptional activity and stability for the oxidation of formic acid.

Ultra‐Large Two‐Dimensional Metal Nanowire Networks by Microfluidic Laminar Flow Synthesis for Formic Acid Electrooxidation

AbstractDespite the great research interest in two‐dimensional metal nanowire networks (2D MNWNs) due to their large specific surface area and abundance of unsaturated coordination atoms, their controllable synthesis still remains a significant challenge. Herein, a microfluidics laminar flow‐based approach is developed, enabling the facile preparation of large‐scale 2D structures with diverse alloy compositions, such as PtBi, AuBi, PdBi, PtPdBi, and PtAuCu alloys. Remarkably, these 2D MNWNs can reach sizes up to submillimeter scale (~220 μm), which is significantly larger than the evolution from the 1D or 3D counterparts that typically measure only tens of nanometers. The PdBi 2D MNWNs affords the highest specific activity for formic acid (2669.1 mA mg−1) among current unsupported catalysts, which is 103.5 times higher than Pt‐black, respectively. Furthermore, in situ Fourier transform infrared (FTIR) experiments provide comprehensive evidence that PdBi 2D MNWNs catalysts can effectively prevent CO* poisoning, resulting in exceptional activity and stability for the oxidation of formic acid.

Ethylenediamine-mediated synthesis of Pd-based catalysts with enhanced electrocatalytic performances towards formic acid oxidation

Pd-based anode catalysts with superior activity are urgent for formic acid oxidation to further boost the direct formic acid fuel cells (DFAFCs) technologies. Herein, a strategy of ethylenediamine (EDA) modified Pd/C catalyst was developed by two main steps of EDA adsorbed on Vulcan XC-72 carbon by impregnation and Pd nanoparticles loaded on the freeze-dried C-EDA supports by liquid reduction method. The effects of sweep rates and concentrations of EDA on the formic acid electrooxidation were systematically studied. Results showed that the above parameter was optimized as the concentration of EDA of 0.1 mol L−1. Pd nanoparticles with even distribution were fabricated and particle sizes were in the range of 3.5–4.2 nm. In addition, Pd particle size became smaller with the addition of EDA, suggesting that EDA could induce the generation of smaller Pd. Electrochemical measurements demonstrated that the electrocatalytic activity of Pd/C-0.22EDA (1021 mA mg−1) with optimized modification concentration was improved as a factor of 3.82 than that of Pd/C (267 mA mg−1). An enhanced stability (about 41 times higher than Pd/C) and faster charge-transfer kinetics of formic acid electrooxidation were observed for Pd/C-0.22EDA catalyst. CV and CA measurements showed that the most active catalyst was made of the smallest (3.5 nm) Pd nanoparticles for Pd/C-0.22EDA catalyst. The better electrocatalytic performances of Pd/C-0.22EDA might be ascribed to evenly dispersed Pd with relatively smaller particle size, electron regulation between Pd and amine group as well as stable Pd structure.

Co and Ni Ratio Modulation‐Derived Electron Deficient Pd Trimetallic Catalysts for Enhanced Formic Acid Electrooxidation

AbstractPdCoNi trimetallic catalysts attracted extensive interest in direct formic acid fuel cells due to high poisoning resistance and high activity for formic acid electro‐oxidation (FAO). Herein, a series of Pd0.75CoxNiy/C alloys with a modulated ratio of Co and Ni are synthesized to investigate the effect of Co and Ni content on the electronic structure of Pd for FAO. The physical analysis demonstrated that the introduction of Co and Ni induces the lattice strain effect compared to monometallic Pd catalysts. As a consequence of fixing the total amount of Co and Ni, the strain effect is restricted, and the electronic perturbation of Pd is successfully regulated by varying the ratio of Co and Ni in Pd0.75CoxNiy/C trimetallic alloys. Pd loses more electrons, the bond strength of Pd−H is weakened, and FAO activity is enhanced first and then decreased as the Co content increases. Among the trimetallic catalysts, Pd0.75Co0.125Ni0.125/C trimetallic catalyst exhibits the highest current density of 3.253 mA cm−2 owing to the optimum electronic perturbation and Pd−H bond strength. This work provides a valuable guideline for future studies of Pd‐based trimetallic alloys.

Stabilizing Diluted Active Sites of Ultrasmall High-Entropy Intermetallics for Efficient Formic Acid Electrooxidation.

The poisoning of undesired intermediates or impurities greatly hinders the catalytic performances of noble metal-based catalysts. Herein, high-entropy intermetallics i-(PtPdIrRu)2FeCu (HEI) are constructed to inhibit the strongly adsorbed carbon monoxide intermediates (CO*) during the formic acid oxidation reaction. As probed by multiple-scaled structural characterizations, HEI nanoparticles are featured with partially negative Pt oxidation states, diluted Pt/Pd/Ir/Ru atomic sites and ultrasmall average size less than 2 nm. Benefiting from the optimized structures, HEI nanoparticles deliver more than 10 times promotion in intrinsic activity than that of pure Pt, and well-enhanced mass activity/durability than that of ternary i-Pt2FeCu intermetallics counterpart. In situ infrared spectroscopy manifests that both bridge and top CO* are favored on pure Pt but limited on HEI. Further theoretical elaboration indicates that HEI displayed a much weaker binding of CO* on Pt sites and sluggish diffusion of CO* among different sites, in contrast to pure Pt that CO* bound more strongly and was easy to diffuse on larger Pt atomic ensembles. This work verifies that HEIs are promising catalysts via integrating the merits of intermetallics and high-entropy alloys.

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.

N-doped hollow carbon nanospheres embedded in N-doped graphene loaded with palladium nanoparticles as an efficient electrocatalyst for formic acid oxidation

Efficient electrocatalysts with a low cost, high activity and good durability play a crucial role in the use of direct formic acid fuel cells. Pd nanoparticles supported on N-doped hollow carbon nanospheres (NHCNs) embedded in an assembly of N-doped graphene (NG) with a three-dimensional (3D) porous structure by a simple and economical method were investigated as direct formic acid fuel cell catalysts. Because of the unique porous configuration of interconnected layers doped with nitrogen atoms, the Pd/NHCN@NG catalyst with Pd nanoparticles has a large catalytic active surface area, superior electrocatalytic activity, a high steady-state current density, and a strong resistance to CO poisoning, far surpassing those of conventional Pd/C, Pd/NG, and Pd/NHCN catalysts for formic acid electrooxidation. When the HCN/GO mass ratio was 1:1, the Pd/NHCN@NG catalyst had an outstanding performance in the catalytic oxidation of formic acid, with an activity 4.21 times that of Pd/C. This work indicates a way to produce superior carbon-based support materials for electrocatalysts, which will be beneficial for the development of fuel cells.

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.

Stabilizing Diluted Active Sites of Ultrasmall High‐Entropy Intermetallics for Efficient Formic Acid Electrooxidation

The poisoning of undesired intermediates or impurities greatly hinders the catalytic performances of noble metal‐based catalysts. Herein, high‐entropy intermetallics i‐(PtPdIrRu)2FeCu (HEI) are constructed to inhibit the strongly adsorbed carbon monoxide intermediates (CO*) during the formic acid oxidation reaction. As probed by multiple‐scaled structural characterizations, HEI nanoparticles are featured with partially negative Pt oxidation states, diluted Pt/Pd/Ir/Ru atomic sites and ultrasmall average size less than 2 nm. Benefiting from the optimized structures, HEI nanoparticles deliver more than 10 times promotion in intrinsic activity than that of pure Pt, and well‐enhanced mass activity/durability than that of ternary i‐Pt2FeCu intermetallics counterpart. In situ infrared spectroscopy manifests that both bridge and top CO* are favored on pure Pt but limited on HEI. Further theoretical elaboration indicates that HEI displayed a much weaker binding of CO* on Pt sites and sluggish diffusion of CO* among different sites, in contrast to pure Pt that CO* bound more strongly and was easy to diffuse on larger Pt atomic ensembles. This work verifies that HEIs are promising catalysts via integrating the merits of intermetallics and high‐entropy alloys.

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.

Kinetics of Formic Acid Electrooxidation on Anodically Modified Silver–Palladium Alloys

Kinetics of Formic Acid Electrooxidation on Anodically Modified Silver–Palladium Alloys

Design of Advanced Thin-Film Catalysts for Electrooxidation of Formic Acid

Design of Advanced Thin-Film Catalysts for Electrooxidation of Formic Acid

High-Entropy Alloy PtCuNiCoMn Nanoparticles on rGO for Electrooxidation of Methanol and Formic Acid.

High-entropy alloy (HEA) nanoparticles have attracted great attention due to their excellent electrocatalytic properties. Herein, PtCuNiCoMn HEA nanoparticles supported on reduced graphene oxide (rGO) are synthesized via a solvothermal co-reduction method and are used as an electrocatalyst for the electrooxidation of methanol and formic acid. Owing to the synergistic effect between the component metals, the high-entropy effect, and the sluggish diffusion effect, the PtCuNiCoMn HEA nanoparticles possess significantly improved electrocatalytic activity and stability compared to PtCuNiCo, PtCuNi, PtCu, Pt nanoparticles, and the commercial Pt/C catalyst. The results reveal the unique advantages of HEA nanoparticles in the field of electrocatalysis. The synthesis method is simple and effective, which may be valuable for the preparation of other HEA electrocatalysts.

The origins of formic acid electrooxidation on selected surfaces of Pt, Pd, and their alloys with Sn

Pd-based trimetallic alloy enhances the catalytic process of formic acid oxidation (FAO) by selectively inhibiting the formation of adsorbed CO*.

Correction: The origins of formic acid electrooxidation on selected surfaces of Pt, Pd, and their alloys with Sn

Correction for ‘The origins of formic acid electrooxidation on selected surfaces of Pt, Pd, and their alloys with Sn’ by Radhey Shyam Yadav et al., J. Mater. Chem. A, 2024, https://doi.org/10.1039/d3ta07219c.

Formic acid electrooxidation on palladium nanostructured electrodes in concentrated solutions

The formic acid oxidation reaction (FAO) was evaluated on palladium nanostructured films supported on glassy carbon in 0.5 M H2SO4 + x M HCOOH solutions, where 0.5 ≤ x ≤ 8.0, in the potential range 0.2 ≤ Es / V ≤ 0.6 vs. RHE at 25 °C. Measurements consisted in chronoamperometric experiments, which were followed by stripping voltammetry in order to evaluate the presence of COad. Open circuit potential (OCP) decay was also employed to analyse the formic acid spontaneous decomposition. The results of OCP experiments showed the formation of β-PdH hydride as well as the absence of COad for all HCOOH concentrations, evidencing that the spontaneous decomposition of HCOOH on palladium is the dehydrogenation reaction, which produces H2 and CO2. It was demonstrated that COad is not directly involved in the kinetic mechanism of the FAO on palladium, and it was also explained the controversy related to the detection of COad in previous studies. Additionally, the highest FAO electrocatalytic activity was observed at x = 2.0 M

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.