Current Oscillations during Formic Acid Oxidation on a Pt Electrode: Insight into the Mechanism by Time-Resolved IR Spectroscopy

Platinum-Lead-Bismuth/Platinum-Bismuth Core/Shell Nanoplate Achieves Complete Dehydrogenation Pathway for Direct Formic Acid Oxidation Catalysis

Designing platinum (Pt)-based formic acid oxidation reaction (FAOR) catalysts with high performance and high selectivity of direct dehydrogenation pathway for direct formic acid fuel cell (DFAFC) is desirable yet challenging. Herein, we report a new class of surface-uneven PtPbBi/PtBi core/shell nanoplates (PtPbBi/PtBi NPs) as the highly active and selective FAOR catalysts, even in the complicated membrane electrode assembly (MEA) medium. They can achieve unprecedented specific and mass activities of 25.1 mA cm^-2 and 7.4 A mg_Pt^-1 for FAOR, 156 and 62 times higher than those of commercial Pt/C, respectively, which is the highest for a FAOR catalyst by far. Simultaneously, they show highly weak adsorption of CO and high dehydrogenation pathway selectivity in the FAOR test. More importantly, the PtPbBi/PtBi NPs can reach the power density of 161.5 mW cm^-2, along with a stable discharge performance (45.8% decay of power density at 0.4 V for 10 h), demonstrating great potential in a single DFAFC device. The in situ Fourier transform infrared spectroscopy (FTIR) and X-ray absorption spectroscopy (XAS) results collectively reveal a local electron interaction between PtPbBi and PtBi. In addition, the high-tolerance PtBi shell can effectively inhibit the production/adsorption of CO, resulting in the complete presence of the dehydrogenation pathway for FAOR. This work demonstrates an efficient Pt-based FAOR catalyst with 100% direct reaction selectivity, which is of great significance for driving the commercialization of DFAFC.

Coupling homogeneous and heterogeneous catalysis for enhancement of HCOOH electrooxidation via the dehydrogenation pathway

The homogeneous/heterogeneous catalyst combination of VO²⁺ in anolyte with Pd/C at the anode is first introduced in a formic acid fuel cell to enhance HCOOH electrooxidation. The VO²⁺/Pd catalyst combination establishes a stepwise reaction pathway involving HCOOH dehydrogenation to form V³⁺ from VO²⁺ reduction and subsequent V³⁺ electrooxidation to regain VO²⁺. The fuel cell with the VO²⁺/Pd combination presents a peak power density of 341.3 mW cm^-2 and stable power density higher than 30 mW cm^-2.

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 mg_Pt ^-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*.

State of Formic Acid Dissolved in Tar According to Infrared Spectroscopy

Formic acid is considered as a promising hydrogen carrier and can be used as a source of hydrogen in the processing of heavy oil fractions such as tar. The interaction of formic acid with tar was studied by infrared Fourier transform spectroscopy via special technique using a mirror substrate. The infrared (IR) spectra were interpreted considering density functional theory (DFT) calculations. It was shown that formic acid dissolved in tar in three forms, as dimers, monomers of cis- and trans-configurations, hydrogen-bonded to the aromatic rings of the tar compounds, and as free-rotating gas molecules (microbubbles in the tar bulk). The research performed provides an opportunity and methodological base for studying the process of tar conversion in the presence of formic acid into gasoline fractions at temperatures up to 300 ^oC.

A Competent MWCNT-Grafted MnOx/Pt Nanoanode for the Direct Formic Acid Fuel Cells

A novel “MnOx/Pt/MWCNT-GC” nanocatalyst is recommended for the electrooxidation of formic acid (EOFA), the principal anodic reaction in the direct formic acid fuel cells (DFAFCs). The sequential (layer-by-layer) protocol was employed to prepare the catalyst through the electrodeposition of Pt (nano-Pt) and manganese oxide (nano-MnOx) nanoparticles onto the surface of a glassy carbon (GC) electrode supported with multiwalled carbon nanotubes (MWCNTs). The nano-MnOx could successfully mediate the mechanism of EOFA by accelerating the charge transfer, “electronic effect”. On the other hand, MWCNTs could enhance the catalytic performance by changing the surface geometry that inhibited the adsorption of poisoning CO, which is a typical intermediate in the reaction mechanism of EOFA that is responsible for the potential deterioration of the catalytic performance of DFAFCs. Interestingly with this modification, a significant enhancement in the catalytic activity and stability toward EOFA was achieved. Several techniques will be employed to evaluate the catalyst’s morphology, composition, crystal structure, and activity and further to understand the role of each of the nano-MnOx and MWCNTs in the catalytic enhancement.

Benchmarking Catalysts for Formic Acid/Formate Electrooxidation

Energy production and consumption without the use of fossil fuels are amongst the biggest challenges currently facing humankind and the scientific community. Huge efforts have been invested in creating technologies that enable closed carbon or carbon neutral fuel cycles, limiting CO2 emissions into the atmosphere. Formic acid/formate (FA) has attracted intense interest as a liquid fuel over the last half century, giving rise to a plethora of studies on catalysts for its efficient electrocatalytic oxidation for usage in fuel cells. However, new catalysts and catalytic systems are often difficult to compare because of the variability in conditions and catalyst parameters examined. In this review, we discuss the extensive literature on FA electrooxidation using platinum, palladium and non-platinum group metal-based catalysts, the conditions typically employed in formate electrooxidation and the main electrochemical parameters for the comparison of anodic electrocatalysts to be applied in a FA fuel cell. We focused on the electrocatalytic performance in terms of onset potential and peak current density obtained during cyclic voltammetry measurements and on catalyst stability. Moreover, we handpicked a list of the most relevant examples that can be used for benchmarking and referencing future developments in the field.

Engineering porous Pd-Cu nanocrystals with tailored three-dimensional catalytic facets for highly efficient formic acid oxidation

Rational synthesis of bi- or multi-metallic nanomaterials with both dendritic and porous features is appealing yet challenging. Herein, with the cubic Cu₂O nanoparticles composed of ultrafine Cu₂O nanocrystals as a self-template, a series of Pd-Cu nanocrystals with different morphologies (e.g., aggregates, porous nanodendrites, meshy nanochains and porous nanoboxes) are synthesized through simply regulating the molar ratio of the Pd precursor to the cubic Cu₂O, indicating that the galvanic replacement and Kirkendall effect across the alloying process are well controlled. Among the as-developed various Pd-Cu nanocrystals, the porous nanodendrites with both dendritic and hollow features show superior electrocatalytic activity toward formic acid oxidation. Comprehensive characterizations including three-dimensional simulated reconstruction of a single particle and high-resolution transmission electron microscopy reveal that the surface steps, defects, three-dimensional architecture, and the electronic/strain effects between Cu and Pd are responsible for the outstanding catalytic activity and excellent stability of the Pd-Cu porous nanodendrites.

Recent advances in formic acid electro-oxidation: from the fundamental mechanism to electrocatalysts

Direct formic acid fuel cells have attracted significant attention because of their low fuel crossover, high safety, and high theoretical power density among all the proton-exchange membrane fuel cells. Much effort has been devoted to the study of formic acid oxidation, including the reaction processes and electrocatalysts. However, as a model reaction, the anodic electro-oxidation process of formic acid is still not very clear, especially regarding the confirmation of the intermediates, which is not helpful for the design and synthesis of high-performance electrocatalysts for formic acid oxidation or conducive to understanding the reaction mechanisms of other small fuel molecules. Herein, we briefly review the recent advances in investigating the mechanism of formic acid electro-oxidation and the basic design concepts of formic acid oxidation electrocatalysts. Rather than an exhaustive overview of all aspects of this topic, this mini-review mainly outlines the progress of this field in recent years.

Ultrathin Film PtxPd(1-x) Alloy Catalysts for Formic Acid Oxidation Synthesized by Surface Limited Redox Replacement of Underpotentially Deposited H Monolayer

This work emphasizes the development of a green synthetic approach for growing ultrathin film PtxPd(1-x) alloy catalysts for formic acid oxidation (FAO) by surface limited redox replacement of underpotentially deposited H sacrificial layer. Up to three-monolayers-thick PtxPd(1-x) films with different composition are generated on Au electrodes and characterized for composition and surface roughness using XPS and electrochemical methods, respectively. XPS results show close correlation between solution molar ratio and atomic composition, with slightly higher Pt fraction in the deposited films. The accordingly deposited Pt42Pd58 films demonstrated remarkable specific and mass activities of up to 35 mAcm−2 and 45 Amg−1 respectively, lasting for more than 1500 cycles in FAO tests. This performance, found to be better twice or more than that of pure Pt counterparts, renders the Pt42Pd58 films comparable with the frontrunner FAO catalysts. In addition, the best alloy catalyst establishes a nearly hysteresis-free FAO CV curve a lot earlier than its Pt counterpart and thus supports the direct FAO pathway for longer. Overall, the combination of high Pd activity and CO tolerance with the remarkable Pt stability results in highly active and durable FAO catalysts. Finally, this facile and cost-effective synthetic approach allows for scaling the catalyst production and is thus appropriate for foreseeable commercialization.

Advances and challenges for experiment and theory for multi-electron multi-proton transfer at electrified solid–liquid interfaces

Understanding microscopic mechanism of multi-electron multi-proton transfer reactions at complexed systems is important for advancing electrochemistry-oriented science in the 21st century.

Phase diagrams and dynamical evolution of the triple-pathway electro-oxidation of formic acid on platinum

A detailed numerical study including stability phase diagrams for the dynamical evolution of the electro-oxidation of formic acid on platinum was reported. The study evidences the existence of intertwined stability phases and the absence of chaos.

Pt and RhPt dendritic nanowires and their potential application as anodic catalysts for fuel cells

Fuel cells have a number of benefits over conventional combustion-based technologies and can be used in a range of important applications, including transportation, as well as stationary, portable and emergency backup power systems. One of the major challenges in this field, however lies in controlling catalyst design which is critical for developing efficient and cost-effective fuel cell technology. Herein, for the first time, we report a facile controlled synthesis of Pt and RhPt dendritic nanowires using ultrathin AuAg nanowires as sacrificial templates. These dendritic nanowires exhibit remarkable catalytic performance in the elecrochemical oxidation of methanol and formic acid. In particular, the RhPt dendritic nanostructures show very high resistance to catalyst poisoning in methanol oxidation. This research demonstrates the advantages of using bimetallic dendritic nanostructures and we believe that these materials and electrocatalytic studies are important for further advancement of fuel cell research and technology.

Active Site-Directed Tandem Catalysis on Single Platinum Nanoparticles for Efficient and Stable Oxidation of Formaldehyde at Room Temperature

The application of tandem catalysis is rarely investigated in degrading organic pollutants in the environment. Herein, a tandem catalyst on single platinum (Pt) nanoparticles (Pt⁰ NPs) is prepared for the sequential degradation of formaldehyde (HCHO) to carbon dioxide gas [CO₂(g)] at room temperature. The synthesis approach includes coating of uniform Pt NPs on SrBi₂Ta₂O₉ platelets using a photoreduction process, followed by calcination of the sample in the atmosphere to tune partial transformation of Pt⁰ atoms to Pt²⁺ ions in the tandem catalyst. The conversion of HCHO to CO₂(g) is monitored by in situ Fourier transform infrared spectroscopy, which shows first conversion of HCHO to CO₃^2- ions onto Pt⁰ active sites and subsequently the conversion of CO₃^2- ions to CO₂(g) by neighboring Pt²⁺ species of the catalyst. The later process with Pt²⁺ species does not allow CO₃^2- poisoning of the catalyst. The enhanced activity of the prepared tandem catalyst to oxidize HCHO is maintained continuously for 680 min. Comparatively, the catalyst without Pt²⁺ shows activity for only 40 min. Additionally, the tandem catalyst presented herein performs better than the Pt/titanium dioxide (TiO₂) catalyst to degrade HCHO. Overall, the tandem catalyst may be applied to degrade organic pollutants efficiently.

Composition dependent activity of PdAgNi alloy catalysts for formic acid electrooxidation

In the present study, the carbon supported Pd, PdAg and PdAgNi (Pd/C, PdAg/C and PdAgNi/C) electrocatalysts are prepared via NaBH₄ reduction method at varying molar atomic ratio for formic acid electrooxidation. These as-prepared electrocatalysts are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma mass spectrometry (ICP-MS), N₂ adsorption-desorption, and X-ray electron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and lineer sweep voltammetry (LSV). While Pd₅₀Ag₅₀/C exhibits the highest catalytic activity among the bimetallic electrocatalyst, it is observed that Pd₇₀Ag₂₀Ni₁₀/C electrocatalysts have the best performance among the all electrocatalysts. Its maximum current density is about 1.92 times higher than that of Pd/C (0.675 mA cm^-2). Also, electrochemical impedance spectroscopy (EIS), chronoamperometry (CA) and lineer sweep voltammetry (LSV) results are in a good agreement with CV results in terms of stability and electrocatalytic activity of Pd₅₀Ag₅₀/C and Pd₇₀Ag₂₀Ni₁₀/C. The Pd₇₀Ag₂₀Ni₁₀/C catalyst is believed to be a promising anode catalyst for the direct formic acid fuel cell.

Formate: A Possible Replacement for Formic Acid in Fuel Cells

We present a facile thermodynamic strategy for identifying formate electrooxidation at a Pt electrode in a fuel cell. Mixtures of formate and sulfuric acid are used as fuel solutions for maintaining formic acid at a low concentration and reducing CO poisoning of the Pt electrode. Pt is modified by a polyaniline porous film to improve the electrocatalytic activity towards formate oxidation. The result indicates that formate can bypass the poisoning path to form CO2 at a low potential. Additionally, we propose a new mechanism of formate electrooxidation and investigate the possibility of an independent oxidation path starting from free formate in solution.

Correlation between Formic Acid Oxidation and Oxide Species on Pt(Bi)/GC and Pt/GC Electrode through the Effect of Forward Potential Scan Limit

Following earlier works from our laboratory, further experiments on electrochemical behavior in formic acid oxidation at electrodeposited Pt(Bi)/GC and Pt/GC electrode were performed in order to examine the effect of successive increase of the forward potential scan limit. Correlation between formic acid oxidation and oxide species on Pt(Bi)/GC electrode with increases of forward potential scan limit is based on the dependency of the backward peak potential from backward peak current. The obtained dependency reveals Bi influence for the scan limits up to 0.8 V. Since the Pt(Bi)/GC electrode is composed of Bi core occluded by Pt and Bi-oxide surface layer, the observed behavior is explained through the influence of surface metal oxide on easier formation of OHad species. Nevertheless, the influence of electronic modification of Pt surface atoms by underlying Bi is present and leads to the stronger adsorption of OH on Pt. At higher forward potential scan limits (from 0.8 V), Pt has a dominant role in HCOOH oxidation.

Ternary Pd–Ni–P hybrid electrocatalysts derived from Pd–Ni core–shell nanoparticles with enhanced formic acid oxidation activity

Highly active formic acid electro-oxidation performance was achieved by using ternary Pd–Ni–P hybrid electro-catalysts with a strong synergistic effect.

Identification of two aliphatic position isomers between α- and β-ketoglutaric acid by using a Briggs-Rauscher oscillating system

This paper reports a novel method for identification of two aliphatic position isomers between α-ketoglutaric acid (α-KA) and β-ketoglutaric acid (β-KA) by their different perturbation effects on a Briggs-Rauscher oscillating system, in which tetraaza-macrocyclic complex [NiL](ClO4)2 is used as the catalyst. The ligand L in the complex is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. The experimental results have shown that addition of α-KA into the system does not affect the oscillating patterns, while the presence of β-KA in a dynamic system influences the oscillatory amplitude. A more interesting feature is that, in the presence of a higher concentration of β-KA, there are damped oscillations after the initial spike, followed by quenching (more exactly: very small oscillations) of the oscillations before the subsequent regeneration of oscillations. A qualitative approach was thus established by employing a Briggs-Rauscher system for identification of these two isomers. The concentrations of these two isomers that can be distinguished lie over the range between 5.0 × 10(-6) and 2.5 × 10(-3) mol/L. A reaction mechanism based on the FCA model has been proposed. An explanation is that β-KA reacts with HOO(•) radicals to form acetone, whereas the α-KA does not.

Formic acid oxidation on platinum: a simple mechanistic study

Formic acid oxidation on Pt(111) under electrocatalytic conditions occurs when a formate anion approaches the Pt(111) surface in the CH-down orientation, and barrierlessly releases carbon dioxide as the H binds to the surface.

Reexamination of formic acid decomposition on the Pt(111) surface both in the absence and in the presence of water, from periodic DFT calculations

The calculated results in literatures for the decomposition of formic acid on Pt(111) into CO cannot rationalize the well-known easy CO poisoning of Pt-based catalysts.