For Formic Acid Oxidation Reaction Research Articles

Cauliflower-like Pd/MoC||Mo2C/C heterostructure as an efficient trifunctional catalyst for formic acid oxidation, hydrogen evolution, and oxygen reduction reactions

The use of Pd-based catalytic materials as electrocatalysts for formic acid oxidation reaction (FAO), hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) has been well-established for some time. The incorporation of a second phase can markedly enhance the electronic properties of the composites. The combination of different compounds with superior electronic properties is crucial for the design and preparation of catalysts with optimal catalytic activity and stability. In this study, a novel cauliflower-like Pd/MoC||Mo2C/C composite with heterostructure is synthesised, which exhibits excellent catalytic activity and long-term stability against FAO, HER, and ORR. The high-temperature treatment results in the formation of small-sized Mo₂C and MoC nanoparticles on the carbonaceous substrate, thereby exposing a greater number of Mo and Mo-C active sites. The formation of heterostructures between Mo₂C and MoC optimises the electronic structure of the composite, thereby facilitating enhanced reaction processes. In terms of FAO, the mass activity of Pd/MoC||Mo2C/C is 1.87A mgPd-1, which is 2.75 times higher than that of Pd/C (0.68A mgPd-1). As for the HER, a much lower overpotential of 28mV is required to achieve a current density of 10mAcm-2 compared to Pd/C (40mV). Fortunately, Pd/MoC||Mo2C/C also shows excellent ORR activity with a half-wave potential of 0.798V and the maximum current density of approximately 5.73mAcm-2 in alkaline electrolyte. These findings may contribute to the development of other noble metal-based materials loaded on intermetallic compounds with stable and effective electrocatalytic performance.

Nanophase-separated ternary PdAgCu nanotubes with rich interfaces for enhanced formic acid oxidation reaction

Herein, a facile strategy for the preparation of PdAgCu ternary nanotubes (NTs) is introduced by using Cu nanowires (NWs) as sacrificial templates along with an acid-leaching treatment. Since the phase separation between Ag and Cu, the obtained PdAgCu NTs is made up of various nanosphases including pure Ag, Cu, bimetallic PdCu and PdAg nanoalloys, instead of PdAgCu trimetallic nanoalloys. By adjusting the types of solvents during synthesis, the surface morphology of PdAgCu NTs can be tuned from smooth (S-PdAgCu NTs) to rough (R-PdAgCu NTs). Both S-PdAgCu NTs and R-PdAgCu NTs exhibit excellent electrocatalytic performances for formic acid oxidation reaction (FAOR). Remarkably, the mass activity of S-PdAgCu NTs for FAOR can reach up to 4307 mA mgPd-1 at peak potential, which is 8.5 times higher than that of commercial Pd (506 mA mgPd-1). The impressively enhanced activity should be ascribed to the synergistic effect of Pd with Cu or Ag and the multi-phase interface engineering, which is resulting from the tight position relationships among different monometallic or bimetallic alloy nanophases.

Designing nanoporous Pd catalyst with dual enhancement of thermodynamics and kinetics for formic acid oxidation reaction

Conventional strategies for developing highly efficient electrocatalysts involve enhancing thermodynamics to minimize overpotential and improving kinetics to maximize reaction current. However, current research on Pd-based catalysts for formic acid oxidation reaction (FAOR) mainly focuses on accelerating its kinetics to increase the peak current. This study proposes a catalyst design that can simultaneously improve the kinetics and thermodynamics of FAOR. Specifically, the home-made catalyst (NPG-Pt1-Pd1) is obtained by sequentially depositing monolayer Pt and Pd shells on the surface of nanoporous gold (NPG) substrate. Compared with commercial Pd/C, this electrocatalyst exhibits a noticeable negative shift in onset potential (∼100 mV) and a significantly improved peak current (∼6 times). Experimental data and theoretical calculations demonstrate that NPG-Pt1-Pd1 exhibits a comparatively suitable adsorption energy for small molecules, not only reducing the overpotential but also accelerating the reaction rate of FAOR. Moreover, when applied in direct formic acid fuel cells (DFAFC), the NPG-Pt1-Pd1 anode with an exceptionally low Pd loading of 8.5 μg cm−2, achieves a remarkable power density of 141 mW cm−2. The power efficiency of Pd is 230 times that of Pd/C (1 mg cm−2, 73 mW cm−2). Therefore, this work provides a new methodology for developing efficient Pd-based FAOR electrocatalysts.

Optimizing dual-intermediates adsorption on Rh-based intermetallics for formic acid electrooxidation

Concurrently optimizing the pathway and electrocatalytic activity for formic acid oxidation reaction (FAOR) is significant but still challenging. Herein, surface and composition engineering strategies are integrated by constructing atomically ordered Rh0.9Pt0.1Fe ternary intermetallic (O-Rh0.9Pt0.1Fe). Supported by the in situ infrared spectra, the carbon monoxide (CO*) mediated indirect FAOR pathway on pure Rh is switched into a direct pathway on RhFe intermetallics (O-RhFe) with isolated Rh atoms, leading to a lower overpotential. Further composition engineering by forming O-Rh0.9Pt0.1Fe contributes to enhanced FAOR activity due to the stabilizing of COOH* intermediate, as indicated by the density functional theory calculations. Besides, O-Rh0.9Pt0.1Fe shows enhanced FAOR activity during potential cycling tests with fewer structural evolutions, while O-RhFe displays a decay. This study provides new insight into tuning reaction pathways and catalytic activity selectively via tailoring adsorption of different intermediates.

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.

The effect of SnO2 on enhancing electrocatalytic property of palladium toward formic acid oxidation

Although palladium (Pd) based materials are considered the best catalyst for formic acid oxidation reaction (FAOR), they are still confronted with a lot of barriers, such as the growth/sintering of Pd nanoparticles (NPs) and the accumulation of adsorbed poisoning intermediates. Herein, tin dioxide (SnO2) decorated carbon black was utilized as the catalyst carrier to synthesize Pd/SnO2/C for FAOR. The introduction of SnO2 significantly reduced the particle size of Pd NPs and forming the Pd–O–Sn structure. Compared with Pd/C, Pd/SnO2/C owned higher concentration of Oads and less adsorption amount of poisoning intermediates. The oxygen atoms adsorbed on Pd surface were rapidly transferred to SnO2 due to the spillover effect. The FAOR reaction kinetic results showed that the introduction of SnO2 accelerated the diffusion rate of formic acid on the electrode surface. Pd/SnO2/C exhibited high specific activity (5.97 mA cm−2), excellent durability, and high anti-CO poisoning ability toward FAOR due to the introduction of SnO2.

Medium/High‐Entropy Amalgamated Core/Shell Nanoplate Achieves Efficient Formic Acid Catalysis for Direct Formic Acid Fuel Cell

AbstractHigh‐entropy alloys (HEAs) have been attracting extensive research interests in designing advanced nanomaterials, while their precise control is still in the infancy stage. Herein, we have reported a well‐defined PtBiPbNiCo hexagonal nanoplates (HEA HPs) as high‐performance electrocatalysts. Structure analysis decodes that the HEA HP is constructed with PtBiPb medium‐entropy core and PtBiNiCo high‐entropy shell. Significantly, the HEA HPs can reach the specific and mass activities of 27.2 mA cm−2 and 7.1 A mgPt−1 for formic acid oxidation reaction (FAOR), being the record catalyst ever achieved in Pt‐based catalysts, and can realize the membrane electrode assembly (MEA) power density (321.2 mW cm−2) in fuel cell. Further experimental and theoretical analyses collectively evidence that the hexagonal intermetallic core/atomic layer shell structure and multi‐element synergy greatly promote the direct dehydrogenation pathway of formic acid molecule and suppress the formation of CO*.

Medium/High-Entropy Amalgamated Core/Shell Nanoplate Achieves Efficient Formic Acid Catalysis for Direct Formic Acid Fuel Cell.

High-entropy alloys (HEAs) have been attracting extensive research interests in designing advanced nanomaterials, while their precise control is still in the infancy stage. Herein, we have reported a well-defined PtBiPbNiCo hexagonal nanoplates (HEA HPs) as high-performance electrocatalysts. Structure analysis decodes that the HEA HP is constructed with PtBiPb medium-entropy core and PtBiNiCo high-entropy shell. Significantly, the HEA HPs can reach the specific and mass activities of 27.2 mA cm-2 and 7.1 A mgPt -1 for formic acid oxidation reaction (FAOR), being the record catalyst ever achieved in Pt-based catalysts, and can realize the membrane electrode assembly (MEA) power density (321.2 mW cm-2 ) in fuel cell. Further experimental and theoretical analyses collectively evidence that the hexagonal intermetallic core/atomic layer shell structure and multi-element synergy greatly promote the direct dehydrogenation pathway of formic acid molecule and suppress the formation of CO*.

Pt Island Decorated Au Anode for Formic Acid Oxidation Reaction

For direct formic acid fuel cell (DFAFC), Pt-based catalyst is widely used as an anode. The Pt catalyst shows high activity and stability for formic acid oxidation reaction (FAOR) in acidic condition. For FAOR, it is generally accepted that Pt follows dual pathway including direct and indirect pathway. During the indirect pathway the Pt surface is vulnerable to CO poisoning, which cause the activity degradation. To enhance the CO tolerance, various Pt-based bi/ternary catalysts have been investigated. In recent, Pt–Au alloy catalysts have reported higher current density for direct FAOR pathway compared with pure Pt catalyst. The enhanced FAOR activity is originated from lower CO adsorption energy. However, the alloy structure has low catalyst utilization, which is not applicable to practical device.In this study, we report Pt islands decorated porous Au electrode for anode of the DFAFC. The porous Au transport layer was fabricated on carbon fiber by galvanic displacement and subsequent electrochemical etching process. Using Au transport layer as a substrate, Pt self-terminated electrodeposition (SED) was performed. By adjusting the SED condition, the Pt loading and coverage on Au surface cab be easily controlled. The FAOR activity test of Pt–Au electrodes was performed by cyclic voltammetry (CV). It was revealed that the current density for direct FAOR is linearly increased as the Pt coverage on Au surface is lower. By increasing the CV cycles, the current density for direct FAOR is gradually increased owing to enhanced ensemble effect. Furthermore, the cycled electrode was applicated into practical DFAFC single cell. The single cell demonstrates more than two-order higher Pt mass activity compared with previously reported single cell using Pt–Au anode.

Galvanic replacement-mediated synthesis of Pd–Cu alloy nanospheres as electrocatalysts for formic acid oxidation

Rational synthesis of bimetallic electrocatalysts with the special geometric structure for direct formic acid fuel cells remains yet challenging. Herein, a facile synthetic strategy is presented to prepare the bimetallic Pd–Cu alloy nanospheres (Pd–Cu ANSs) catalysts based on the galvanic replacement and high-temperature reconstruction. The formation mechanism of Pd–Cu ANSs is studied thoroughly from comprehensive characterizations and control experiments. The optimized Pd–Cu ANSs with unique nanosphere structure as well as regulated electronic structure provide excellent electrocatalytic performance for formic acid oxidation reaction (FAOR) with a specific activity of 6.11 mA cm-2Pd and mass activity of 1569.48 mA mg-1Pd, which are 2.7 times and 3.5 times as high as these of the Pd/C catalyst. This synthetic method outlined here could provide a new pathway for noble metal-based alloy nanomaterials for diverse applications.

Hierarchical core-shell Ni-Co-Cu-Pd alloys for efficient formic acid oxidation reaction with high mass activity

Development of efficient electrocatalyst with a small use of noble metals for formic acid oxidation reaction (FAOR) is the most urgent need in realizing practical direct formic acid fuel cells (DFAFC). Herein, we developed quaternary Ni-Co-Cu-Pd (NCCP) alloys with an intriguing nanostructure, that is, hierarchical core–shell structure, which demonstrates excellent catalytic performance for FAOR with a high mass activity. The mass activity of NCCP for FAOR is 3 folds higher than the benchmark Palladium on Carbon (Pd/C, 10 wt%) catalyst. We reason this exceptionally high mass activity of NCCP to the synergetic effects between the surface decorated Pd nanoclusters and the transition metal cores, resulting in highly disturbed electronic configurations at the surface. In addition, the intriguing nanostructure evolved during FAOR can facilitate atomic, ionic, and molecular transfers during FAOR. The NCCP also demonstrates a high electrocatalytic stability for FAOR, which highlights its potential use for the practical DFAFC.

Au core-PtAu alloy shell nanowires for formic acid electrolysis

Inefficient electrocatalysts and high-power consumption are two thorny problems for electrochemical hydrogen (H2) production from acidic water electrolysis. Herein we report the one-pot precise synthesis of ultrafine Au core-PtAu alloy shell nanowires (Au@PtxAu UFNWs). Among them, Au@Pt0.077Au UFNWs exhibit the best performance for formic acid oxidation reaction (FAOR) and hydrogen evolution reaction (HER), which only require applied potentials of 0.29 V and −22.6 mV to achieve a current density of 10 mA cm−2, respectively. The corresponding formic acid electrolyzer realizes the electrochemical H2 production at a voltage of only 0.51 V with 10 mA cm−2 current density. Density functional theory (DFT) calculations reveal that the Au-riched PtAu alloy structure can facilitates the direct oxidation pathway of FAOR and consequently elevates the FAOR activity of Au@Pt0.077Au UFNWs. This work provides meaningful insights into the electrochemical H2 production from both the construction of advanced bifunctional electrocatalysts and the replacement of OER.

Bidirectional controlling synthesis of branched PdCu nanoalloys for efficient and robust formic acid oxidation electrocatalysis

Through a two-way control of hexadecyl trimethyl ammonium bromide (CTAB) and hydrochloric acid (HCl), the PdCu nanoalloys with branched structures are synthesized in one step by hydrothermal reduction and used as electrocatalysts for formic acid oxidation reaction (FAOR). In this two-way control strategy, the CTAB is used as a structure-oriented surfactant, while a certain amount of HCl is used to control the reaction kinetics for achieving gradual growth of multi-dendritic structures. The characterizations including scanning transmission electron microscope (STEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) suggest that PdCu nanoalloys with unique multi-dendritic branches have favorable electronic structure and lattice strain for electrocatalyzing the oxidation of formic acid. In specific, among the electrocatalysts with different Pd/Cu ratios, the Pd1Cu1 branched nanoalloys have the largest electrochemically active surface area (ECSA) and the best performance for the FAOR. The catalytic activity of the Pd1Cu1 branched nanoalloys is 2.4 times that of commercial Pd black. After the chronoamperometry test, the Pd1Cu1 branched nanoalloys still maintain their original morphologies and higher current density than that of the commercial Pd black. In addition, in the CO-stripping tests, the initial oxidation potential and the oxidation peak potential of the PdCu branched nanoalloys for CO adsorption are lower than those of commercial Pd balck, evincing their better anti-poisoning performance.

Continuous and conformal thin TiO2-coating on carbon support makes Pd nanoparticles highly efficient and durable electrocatalyst

Improving the activity and durability of Pd or Pt nanoparticle (NP) electrocatalyst is an urgent issue for the widespread use of fuel cells. In order to achieve high catalytic activity, incorporation of metal oxides into electrocatalysts has been pursued, mainly for the purpose of enabling strong metal-support interaction (SMSI) between the NPs and metal oxides. In this study, we demonstrate a novel method to coat TiO2 on carbon nanotubes (CNTs) through sonochemical reaction of TiO(acac)2 (acac = acetyl acetate) in dimethyl sulfoxide (DMSO). The TiO2-coated CNT (TC(S)) is characterized by a continuous conformal TiO2-coating with the thickness of ∼1.5 nm throughout without any exposed CNT surface. The same reaction in ethylene glycol (EG) or N, N-dimethylformamide (DMF) also produced TCs (TC(E) and TC(F), respectively), but without the conformity and/or continuity seen in TC(S). Formation of Pd NPs on TC by a second sonochemical reaction in EG results in Pd/TC electrocatalysts with significantly increased activity and durability for formic acid oxidation reaction (FAOR) from the reference Pd NPs on CNT. Pd/TC(S) shows the highest activity and durability, surpassing all in the literature data. The enhanced FAOR activity of Pd/TC(S) can be attributed to the SMSI effect from the interface between Pd NPs and TiO2-coating plus the bifunctional mechanism of TiO2. The increased durability can be explained as the result of protecting CNT against the corrosion from CNT-Pd contact.

Electronic structure control over Pd nanorods by B, P-co-doping enables enhanced electrocatalytic performance

The popularization and commercialization of direct formic acid fuel cells require the development of superior electrocatalysts for formic acid oxidation reaction (FAOR). Herein, we report a ternary metal-metalloid-nonmetal PdBP catalyst that was fabricated via the co-doping of B and P elements into pre-synthesized Pd nanorods. Due to the coordinated enhancement of its rod-like structure and the doping of B and P, the structural and compositional advantages of ternary PdBP nanorods (PdBP NRs) can synergistically improve the electrocatalytic FAOR, achieving a mass activity of 1.32 mA μgPd−1 and a specific activity of 4.58 mA cm−2, which is superior to Pd NRs, PdB NRs, PdP NRs and commercial Pd black. This study may spotlight a compositional engineering avenue to develop newly advanced doped metal-based catalysts for electrocatalysis systems.

Stable and Efficient PtRu Electrocatalysts Supported on Zn-BTC MOF Derived Microporous Carbon for Formic Acid Fuel Cells Application.

Highly efficient, well-dispersed PtRu alloy nanoparticles supported on high surface area microporous carbon (MPC) electrocatalysts, are prepared and tested for formic acid oxidation reaction (FAOR). The MPC is obtained by controlled carbonization of a zinc-benzenetricarboxylate metal-organic framework (Zn-BTC MOF) precursor at 950°C, and PtRu (30 wt.%) nanoparticles (NPs) are prepared and deposited via a polyol chemical reduction method. The structural and morphological characterization of the synthesized electrocatalysts is carried out using powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), an energy dispersive X-ray (EDX) technique, and gas adsorption analysis (BET). The FAOR performance of the catalysts is investigated through cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). A correlation between high electrochemical surface area (ECSA) and high FAOR performance of the catalysts is observed. Among the materials employed, Pt1Ru2/MPC 950 with a high electrochemical surface area (25.3 m2 g−1) consequently showed superior activity of the FAOR (Ir = 9.50 mA cm−2 and Jm = 2,403 mA ) at room temperature, with improved tolerance and stability toward carbonaceous species. The superior electrochemical performance, and tolerance to CO-poisoning and long-term stability is attributed to the high surface area carbon support (1,455 m2 g−1) and high percentage loading of ruthenium (20 wt.%). The addition of Ru promotes the efficiency of electrocatalyst by offering FAOR via a bifunctional mechanism.

Metal-organic interface engineering for boosting the electroactivity of Pt nanodendrites for hydrogen production

Abstract Recently, the surface chemical functionalization and morphology control of precious metal nanostructures have been recognized as two efficient strategies for improving their electroactivity and/or selectivity. In this work, 1, 10-phenanthroline monohydrate (PM) functionalized Pt nanodendrites (Pt-NDs) on carbon cloth (CC) (denoted as PM@Pt-NDs/CC) and polyethylenimine (PEI) functionalized Pt-NDs on CC (denoted as PEI@Pt-NDs/CC) are successfully achieved by immersing Pt-NDs/CC into PM and PEI aqueous solutions, respectively. PEI functionalization of Pt-NDs/CC improves its electroactivity for hydrogen evolution reaction (HER) due to local proton enrichment whereas PM functionalization of Pt-NDs/CC improves its electroactivity for formic acid oxidation reaction (FAOR) by facilitating dehydrogenation pathway. With such high activity, a two-electrode electrolyzer is assembled using PM@Pt-NDs/CC as the anodic electrocatalyst and PEI@Pt-NDs/CC as the cathodic electrocatalyst for electrochemical reforming of formic acid, which only requires 0.45 V voltage to achieve the current density of 10 mA cm−1 for high-purity hydrogen production, much lower than conventional water electrolysis (1.59 V). The work presents an example of interfacial engineering enhancing electrocatalytic activity and indicates that electrochemical reforming of formic acid is an energy-saving electrochemical method for high-purity hydrogen production.

Fabrication of polyaniline/SBA-15-supported platinum/cobalt nanocomposites as promising electrocatalyst for formic acid oxidation

In this paper, polyaniline/SBA-15 (PANI/SBA-15) nanocomposites were successfully synthesized as substrates for platinum–cobalt (PtCo) alloy. The PANI/SBA-15 was prepared via in situ emulsion polymerization, and PtCo nanocatalyst was fabricated through a simple electrodeposition method. Subsequently, the synthesized nanocomposites were characterized by SEM, FT-IR spectroscopy, and XRD techniques. The fabricated nanostructure (PtCo/PANI/SBA-15) was then employed as electrode for formic acid oxidation reaction (FAOR). Several samples of PANI/SBA-15-supported PtCo electrocatalysts were synthesized by varying the Co precursor concentration in the electrodeposition solution. The PtCo 0.05/PANI/SBA-15 sample revealed outstanding electrocatalytic activity and stability for FAOR. Based on cyclic voltammetry (CV) measurements, this electrocatalyst generated a maximum current density of about 63 mA cm−2 in the forward potential scan, which is highly desirable for FAOR improvement. Additionally, the PtCo 0.05/PANI/SBA-15 resulted in good performance in ethanol and methanol oxidation, indicating its capability of being applied in other fuel cell technologies.

Highly Active and Durable Ordered Intermetallic PdFe Electrocatalyst for Formic Acid Electrooxidation Reaction

In this paper, we report the preparation of highly active and durable ordered intermetallic PdFe catalyst supported on carbon black for formic acid oxidation reaction (FAOR) by high-temperature hea...

Three-dimensional hierarchical urchin-like PdCuPt nanoassembles with zigzag branches: A highly efficient and durable electrocatalyst for formic acid oxidation reaction

Hierarchically branched multi-metallic nanoassembles are promising catalysts extensively used in catalytic fields because of their unique structural features and multicompositions advantages. Herein, three-dimensional (3D) hierarchical zigzag-branched urchin-like PdCuPt superstructures (HZBUS) were prepared by a one-pot wet-chemical method, where polyethylene oxide (PEO) and KBr served as directing agents. The specific architectures provided abundant active sites highly available for reactants, in turn showing highly enlarged electrochemically active surface area (16.79 m2 g−1Pd). The as-obtained PdCuPt HZBUS displayed dramatically enhanced catalytic activity and improved long-term durability for formic acid oxidation reaction (FAOR), surpassing homemade PdCu nanoparticles (NPs), commercial Pd black and Pt/C catalysts. This work offers a new strategy for construction of advanced multimetallic electrocatalysts with charming superstructures and high-efficient performances in fuel cells.