Concentrations Of HCOOH Research Articles

Optimizing Cr(VI) reduction to Cr(III) using Pd-CNTs nanocatalyst: kinetic Monte Carlo simulation and experimental design insights

In this investigation, we explored the kinetics of Cr(VI) reduction to Cr(III) on carbon nanotube decorated with palladium (Pd-CNTs) nanocatalyst, using formic acid as the reducing agent. This study has been bone utilizing kinetic Monte Carlo simulation and experimental design methods. The mechanism and kinetic parameters of this reaction are provided. The effect various factors such as reaction time, pH level, dichromate (Cr2O72−) concentration, and formic acid concentration on Cr(VI) reduction was studied. Concentrations of HCOOH and Cr2O72− were identified as the crucial variables, while the HCOOH concentration has the most significant impact. Positive influences on Cr(VI) reduction were observed with increasing pH level and HCOOH concentration. Reaction time positively affects on Cr(VI) reduction efficiency. However, the concentration of Cr2O72− showed an increasing effect up to a threshold, negatively impacting the efficiency. The optimal conditions (Reaction time = 60 min, pH = 4.5, [Cr2O72−] = 5.05 × 10−3 M, and [HCOOH] = 0.95 M) for Cr(VI) reduction. At optimal conditions, the Cr(VI) reduction efficiency was obtained to be 100%.

Efficient Photochemical Vapor Generation from Low Concentration Formic Acid Media.

Herein, we report on surprisingly efficient photochemical vapor generation (PVG) of Ru, Re, and especially Ir, achieved from very dilute HCOOH media employing a thin-film flow-through photoreactor operated in flow injection mode. In the absence of added metal ion sensitizers, efficiencies near 20% for Ir and approximately 0.06% for Ru and Re occur in a narrow range of HCOOH concentrations (around 0.01 M), significantly higher than previously reported from conventionally optimized HCOOH concentrations (1-20 M). A substantial enhancement in efficiency, to around 9 and 1.5%, could be realized for Ru and Re, respectively, when 0.005 M HCOONa served as the PVG medium. The addition of metal ion sensitizers (particularly Cd2+ and Co2+) to 0.01 M HCOOH significantly enhanced PVG efficiencies to 17, 2.2, and 81% for Ru, Re, and Ir, respectively. Possible mechanistic aspects occurring in dilute HCOOH media are discussed, wherein this phenomenon is attributed to the action of 185 nm radiation available in the thin-film flow-through photoreactor. An extended study of PVG of Fe, Co, Ni, As, Se, Mo, Rh, Te, W, and Bi from both dilute HCOOH and CH3COOH was undertaken, and several elements for which a similar phenomenon appears were identified (i.e., Co, As, Se, Te, and Bi). Although use of dilute HCOOH media is attractive for practical analytical applications employing PVG, it is less tolerant toward dissolved gases and interferents in the liquid phase due to the likely lower concentrations of free radicals and aquated electrons required for analyte ion reduction and product synthesis.

Photochemical ageing of aerosols contributes significantly to the production of atmospheric formic acid

Abstract. Formic acid (HCOOH) is one of the most abundant organic acids in the atmosphere and affects atmospheric acidity and aqueous chemistry. However, the HCOOH sources are not well understood. In a recent field study, we measured atmospheric HCOOH concentrations at a coastal site in southern China. The average concentrations of HCOOH were 191 ± 167 ppt in marine air masses and 996 ± 433 ppt in coastal air masses. A strong linear correlation between HCOOH concentrations and the surface area densities of submicron particulate matter was observed in coastal air masses. Post-campaign laboratory experiments confirmed that the photochemical ageing of ambient aerosols promoted by heterogeneous reactions with ozone produced a high concentration of HCOOH at a rate of 0.185 ppb h−1 under typical ambient conditions at noon. HCOOH production was strongly affected by nitrate photolysis, as this efficiently produces OH radicals that oxidise organics to form HCOOH. We incorporated this particle-phase source into a photochemical model, and the net HCOOH production rate increased by about 3 times compared with the default Master Chemical Mechanism (MCM). These findings demonstrate that the photochemical ageing of aerosols is an important source of HCOOH that should be included in atmospheric chemistry–transport models.

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

HCOOH in the remote atmosphere: Constraints from Atmospheric Tomography (ATom) airborne observations.

Formic acid (HCOOH) is an important component of atmospheric acidity but its budget is poorly understood, with prior observations implying substantial missing sources. Here we combine pole-to-pole airborne observations from the Atmospheric Tomography Mission (ATom) with chemical transport model (GEOS-Chem CTM) and back trajectory analyses to provide the first global in-situ characterization of HCOOH in the remote atmosphere. ATom reveals sub-100 ppt HCOOH concentrations over most of the remote oceans, punctuated by large enhancements associated with continental outflow. Enhancements correlate with known combustion tracers and trajectory-based fire influences. The GEOS-Chem model underpredicts these in-plume HCOOH enhancements, but elsewhere we find no broad indication of a missing HCOOH source in the background free troposphere. We conclude that missing non-fire HCOOH precursors inferred previously are predominantly short-lived. We find indications of a wet scavenging underestimate in the model consistent with a positive HCOOH bias in the tropical upper troposphere. Observations reveal episodic evidence of ocean HCOOH uptake, which is well-captured by GEOS-Chem; however, despite its strong seawater undersaturation HCOOH is not consistently depleted in the remote marine boundary layer. Over fifty fire and mixed plumes were intercepted during ATom with widely varying transit times and source regions. HCOOH:CO normalized excess mixing ratios in these plumes range from 3.4 to >50 ppt/ppb CO and are often over an order of magnitude higher than expected primary emission ratios. HCOOH is thus a major reactive organic carbon reservoir in the aged plumes sampled during ATom, implying important missing pathways for in-plume HCOOH production.

Investigation on Electroreduction of CO2 to Formic Acid Using Cu3(BTC)2 Metal-Organic Framework (Cu-MOF) and Graphene Oxide.

A recent class of porous materials, viz., metal–organic frameworks (MOFs), finds applications in several areas. In this work, Cu-based MOFs (Cu–benzene-1,3,5-tricarboxylic acid) along with graphene oxide, viz., Cu-MOF/GO, are synthesized and used further for reducing CO2 electrochemically. The reduction was accomplished in various supporting electrolytes, viz., KHCO3/H2O, tetrabutylammonium bromide (TBAB)/dimethylformamide (DMF), KBr/CH3OH, CH3COOK/CH3OH, TBAB/CH3OH, and tetrabutylammonium perchlorate (TBAP)/CH3OH to know their effect on product formation. The electrode fabricated with the synthesized material was used for testing the electroreduction of CO2 at various polarization potentials. The electrochemical reduction of CO2 is carried out via the polarization technique within the experimented potential regime vs saturated calomel electrode (SCE). Ion chromatography was employed for the analysis of the produced products in the electrolyte, and the results showed that HCOOH was the main product formed through reduction. The highest concentrations of HCOOH formed for different electrolytes are 0.1404 mM (−0.1 V), 66.57 mM (−0.6 V), 0.2690 mM (−0.5 V), 0.2390 mM (−0.5 V), 0.7784 mM (−0.4 V), and 0.3050 mM (−0.45 V) in various supporting electrolyte systems, viz., KHCO3/H2O, TBAB/DMF, KBr/CH3OH, CH3COOK/CH3OH, TBAB/CH3OH, and TBAP/CH3OH, respectively. The developed catalyst accomplished a significant efficiency in the conversion and reduction of CO2. A high faradic efficiency of 58% was obtained with 0.1 M TBAB/DMF electrolyte, whereas for Cu-MOF alone, the efficiency was 38%. Thus, the work is carried out using a cost-effective catalyst for the conversion of CO2 to formic acid than using the commercial electrodes. The synergistic effect of GO sheets at 3 wt % concentration and Cu+OH– interaction leads to the formation of formic acid in various electrolytes.

Aromatic Photo-oxidation, A New Source of Atmospheric Acidity.

Formic acid (HCOOH), one of the most important and ubiquitous organic acids in the Earth's atmosphere, contributes substantially to atmospheric acidity and affects pH-dependent reactions in the aqueous phase. However, based on the current mechanistic understanding, even the most advanced chemical models significantly underestimate the HCOOH concentrations when compared to ambient observations at both ground-level and high altitude, thus underrating its atmospheric impact. Here we reveal new chemical pathways to HCOOH formation from reactions of both O3 and OH with ketene-enols, which are important and to date undiscovered intermediates produced in the photo-oxidation of aromatics and furans. We highlight that the estimated yields of HCOOH from ketene-enol oxidation are up to 60% in polluted urban areas and greater than 30% even in the continental background. Our theoretical calculations are further supported by a chamber experiment evaluation. Considering that aromatic compounds are highly reactive and contribute ca. 10% to global nonmethane hydrocarbon emissions and 20% in urban areas, the new oxidation pathways presented here should help to narrow the budget gap of HCOOH and other small organic acids and can be relevant in any environment with high aromatic emissions, including urban areas and biomass burning plumes.

Composition and Structure of Hydrates Formed in Aqueous Solutions of Formic Acid

IR spectroscopy and quantum chemical methods are used to study the features of hydration and determine concentration structural areas in the HCOOH-H2O system. Data on the composition and structure of stable heteroassociates (HA) formed in HCOOH aqueous solutions are obtained from the joint analysis of the IR spectra of these solutions and the results of quantum chemical calculations of (HCOOH)m·(H2O)n (m = 1−4, 6, n = 1−10, 14) and HCO 2 − ·(H2O)n (n = 2, 6) complexes. The sequence is established in which these complexes form when pure acid is diluted with water. For HCOOH concentrations from 100% to the ratio HCOOH:H2O = 1:1, all water molecules are involved in the most stable cyclic (HCOOH)2· (H2O)2 HAs with the C2 symmetry. The components of the equimolar solution are almost completely bound into such hydrates. For the HCOOH:H2O ratio ranging from 1:1 to 1:2, less stable (by ∼10%) cyclic HCOOH · (H2O)2 HAs form along with the (HCOOH)2 · (H2O)2 complexes. The solution with a twofold water excess consists of these hydrates. A further increase in the water concentration results in further hydration of HCOOH · (H2O)2 HAs.

Electrochemical conversion of CO2 to HCOOH at tin cathode in a pressurized undivided filter-press cell

The electrochemical reduction of carbon dioxide to formic acid was performed for the first time in a pressurized filter-press cell with a continuous recirculation of the electrolytic solution (0.9 L) at a tin cathode. It was shown that the performances of the system are comparable or slightly better than that of a batch system with a smaller volume (0.05 L). The selection of proper values of both current density and CO2 pressure allowed to achieve quite high values of faradaic efficiencies. Long-time electrolyses have shown that the system is stable and that it can allow to generate quite high concentrations of HCOOH (about 0.4 M).

Supercritical Hydrothermal Synthesis of Ultra-Fine Copper Particles Using Different Precursors

Supercritical hydrothermal synthesis is a green synthesis method for metal and metal oxide ultra-fine particles. Ultra-fine copper particles are of great interests for the researchers because of the excellent performance in recent years. In this paper, supercritical hydrothermal synthesis of copper ultra-fine particles with three different precursors (CuSO4, Cu(NO3)2, Cu(HCOO)2) are reported. This thesis reports that different products are produced with different precursors. Also, three kinds of reaction mechanisms with different precursors in supercritical water were explained. The conversion of copper ions in the reaction of Cu(HCOO)2 in supercritical water is the highest, the value reaches 100.0%. In the process of synthesizing ultra-fine copper particles, different additional HCOOH concentrations (0, 0.1 mol/L, 0.2 mol/L) and different reaction times (5 mins, 10 mins) were applied. Zero-valent ultra-fine copper particles without impurity were synthesized. The synthesized copper ultra-fine particles were cubic aggregations with micro-meter size

Pd/MWNTs Nanocatalysts Toward Formic Acid Oxidation

Operating conditions such as the composition of electrolyte and temperature can greatly influence the performance of formic acid oxidation reaction (FAOR). In order to achieve the best performance at various conditions, we employed an as-synthesized high electrocatalytic palladium decorated multi-walled carbon nanotubes nanocatalysts (Pd/MWNTs) to investigate the effects of formic acid (HCOOH) and sulfuric acid (H2SO4) concentrations as well as temperature on FAOR. Electro-characterization techniques such as cyclic voltammetry (CV) and slow linear sweep voltammetry (SLV) were employed to comprehensively investigate the catalyst performance and reaction kinetics, which indicate that the as-synthesized Pd/MWNTs gave the best performance under a condition with balanced adsorptions of HCOOH and H2SO4 molecules, and increasing temperature has a positive effect on FAOR. Two well acknowledged reaction pathways of FAOR as dehydrogenation and dehydration were detailed characterized by chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) conducted at various potentials. The dehydrogenation pathway was largely depressed by the increased dehydration pathway, which leads to the increased charge transfer resistance (Rct ) with increasing the relative ratio of HCOOH to H2SO4 concentration. Enhanced tolerance stability and reduced Rct with increasing temperature is observed due to the enhanced reaction kinetics which simultaneously increased the dehydration process. Experimental Briefly, 100.0 mg MWNTs was dispersed with 50 mL xylene in a 100 mL beaker under ultra-sonication for 1 hour, after which the MWNTs/xylene mixture was transferred into a 250 mL 3-neck flask. Then, the solution was heated to reflux ( ~140 °C) after 20 min. At the meantime, 304.0 mg Pd(AcAc)2was dispersed with 20 mL xylene in a 50 mL beaker under magnetic stirring for 10 min, and the mixture was then transferred into the 3-neck flask. The whole solution was then kept refluxing for an additional 3 hours to complete the reaction. After that, the final solution was cooled down to room temperature naturally, filtered under vacuum and rinsed with ethanol and distilled water 3 times, respectively. The final product (black powders) was collected after vacuum drying at 50 °C for 24 hours. Results and Discussion Pd NPs were uniformly dispersed and anchored on the MWNTs support due to the promoting function of carboxylic groups on the surface of MWNTs, which is demonstrated by TEM, Raman and XPS spectra. The hydrogen adsorption and the oxidation of poisoning species processes during the potential sweeping are essential for the enhancement of electroactivity. The main oxidation process shifts between dehydrogenation and dehydration with varying the ratio of HCOOH to H2SO4 concentration, which is illustrated by the variation of oxidation peak potential and current. Greatly facilitated reaction kinetics are demonstrated by the increased oxidation current and decreased charge transfer resistance with increasing temperature. Conclusion Pd/MWNTs as a representative of the Pd-based catalyst were employed to investigate the FAOR mechanism and poisoning effect on Pd/MWNTs electrode in H2SO4 solution. It is demonstrated that the hydrogen adsorption in low potential range and the oxidation of poisoning species during the high potential range both contribute to the enhancement of electroactivity of Pd/MWNTs. The dual pathway mechanism are comprehensively studied by CA and EIS which indicate that the oxidation of HCOOH through dehydrogenation pathway only proceeded in conditions with relatively lower HCOOH and H2SO4 concentrations. Increasing HCOOH concentration can directly increase the dehydration process proportion and cause the production of COads species. H2SO4 as donor of H+ can greatly facilitate the on-set oxidation of HCOOH in the beginning process but it will largely depress the HCOOH oxidation with excess amount of H+. Finally, increasing temperature can boast the mobility of ions thus enhance the reaction kinetics. Dehydration pathway is also existed at higher temperature due to the increasing produced COads species. Acknowledgments The financial supports from University of Tennessee Knoxville are kindly acknowledged. Figure 1. CV of the formic acid oxidation reaction on the Pd/MWNTs electrode in 0.5 M H2SO4 solution containing 0.2 M HCOOH. Background shows the TEM image of the Pd/MWNTs.

Heterogeneous photocatalytic removal of U(VI) in the presence of formic acid: U(III) formation

The efficiency of TiO2 heterogeneous photocatalysis under UV–visible light for removal of uranyl (UO22+) (0.25mM, pH 3) in the presence of formic acid (HCOOH) was investigated. The effect of the counterion of the uranium salt (perchlorate and acetate–nitrate) and the use of quartz and glass photoreactors were analyzed. The transformation of U(VI) in the presence of HCOOH was significantly high and the best removal conditions have been established. The highest efficiency was observed for uranyl perchlorate in the quartz photoreactor with 0.001M HCOOH, while uranyl acetate yielded a lower removal. HCOOH concentrations >0.01M provoked uranium reoxidation. U(VI) photocatalytic transformation was also studied by direct spectrophotometry using TiO2 nanoparticles in the presence of 1M HCOOH at pH<2. U(V), U(IV) and U(III) were detected. U(III) formation was also apparent in the absence of the photocatalyst. This is the first time that formation of U(III) in a photochemical U(VI) system is reported.

Photocatalytic degradation of chlorinated propenes using TiO2

The photocatalytic degradation of chlorinated propenes using TiO2 was investigated by FTIR spectroscopy. The chlorinated propenes were degraded to HCl, CO2, CO, H2O, and HCOOH during UV irradiation. During the degradation of 3-chloro-1-propene, the concentrations of CO2, CO, and HCOOH increased just after starting the irradiation. The onset of the HCl formation was delayed. On the other hand, the onset of the HCOOH formation was delayed during the degradation of 1-chloro-1-propene. During the degradation of 2-chloro-1-propene, the rate of the HCOOH production was slower than that during the degradation of 3-chloro-1-propene although the HCl production was not delayed. These results indicated that HCOOH was produced by the degradation of the double-bonded carbon bonding to two H atoms during the initial stage. The chlorinated compounds were preferentially produced from the double-bonded carbon bonding to the Cl atom and rapidly degraded to HCl, CO2, and CO during the initial stage. The residual part was degraded in the latter steps. Furthermore, it is suggested that the Cl atom on one of the double-bonded C atoms of the propenes was transferred to the other C atom before the degradation. Consequently, the double-bonded carbon bonding to two H atoms in 2-chloro-1-propene was chlorinated, then degraded to HCl, CO2, and CO during the initial stage.

Reactions of atomic hydrogen with formic acid and carbon monoxide in solid parahydrogen I: Anomalous effect of temperature.

Low-temperature condensed phase reactions of atomic hydrogen with closed-shell molecules have been studied in rare gas matrices as a way to generate unstable chemical intermediates and to study tunneling-driven chemistry. Although parahydrogen (pH2) matrix isolation spectroscopy allows these reactions to be studied equally well, little is known about the analogous reactions conducted in a pH2 matrix host. In this study, we present Fourier transform infrared (FTIR) spectroscopic studies of the 193 nm photoinduced chemistry of formic acid (HCOOH) isolated in a pH2 matrix over the 1.7 to 4.3 K temperature range. Upon short-term irradiation the HCOOH readily undergoes photolysis to yield CO, CO2, HOCO, HCO and H atoms. Furthermore, after photolysis at 1.9 K tunneling reactions between migrating H atoms and trapped HCOOH and CO continue to produce HOCO and HCO, respectively. A series of postphotolysis kinetic experiments at 1.9 K with varying photolysis conditions and initial HCOOH concentrations show the growth of HOCO consistently follows single exponential (k = 4.9(7)x10(-3) min(-1)) growth kinetics. The HCO growth kinetics is more complex displaying single exponential growth under certain conditions, but also biexponential growth at elevated CO concentrations and longer photolysis exposures. By varying the temperature after photolysis, we show the H atom reaction kinetics qualitatively change at ∼2.7 K; the reaction that produces HOCO stops at higher temperatures and is only observed at low temperature. We rationalize these results using a kinetic mechanism that involves formation of an H···HCOOH prereactive complex. This study clearly identifies anomalous temperature effects in the reaction kinetics of H atoms with HCOOH and CO in solid pH2 that deserve further study and await full quantitative theoretical modeling.

Formic Acid Electrooxidation on Noble‐Metal Electrodes: Role and Mechanistic Implications of pH, Surface Structure, and Anion Adsorption

AbstractThe influence of the electrolyte pH on formic acid (HCOOH) electrooxidation is investigated on both polycrystalline Pt and Au electrodes and on single‐crystalline Au electrodes in perchloric and sulfuric acid‐based electrolytes. On Au electrodes, the potentiodynamic oxidation currents are found to depend, in a nonlinear way, on the electrolyte pH in a bell‐shaped relation, with a maximum of the catalytic activity at the pKa of HCOOH. On polycrystalline Pt electrodes, this feature is not observed; the catalytic activity increases steadily with increasing pH up to a pH value of approximately 5, which is followed by a plateau until pH 10, in contrast with recent observations [J. Joo, T. Uchida, A. Cuesta, M. T. M. Koper, M. Osawa, J. Amer. Chem. Soc.­ 2013, 135, 9991–9994]. In addition, for Au surfaces, the reaction is only weakly influenced by the electrode surface structure, whereas for Pt, structural effects are known to be considerable. Anion effects, in contrast, are much stronger for the reaction on Au electrodes compared to Pt electrodes. Also, it is shown that Pt‐group‐metal‐free Au electrodes do not oxidize molecular hydrogen under reaction conditions. The results are discussed in relation to findings in previous mechanistic studies. Most importantly, the activity on both electrodes is closely correlated with the concentration of HCOO−, and for Au correlates with both HCOO− and HCOOH concentrations. Based on these results, a number of mechanistic proposals put forward in earlier studies must be discarded, and examples for mechanisms compatible with these results are discussed.

Activity of Pd/C for hydrogen generation in aqueous formic acid solution

A commercial Pd/C catalyst was found to exhibit high activity for formic acid (HCOOH) decomposition into CO2 and H2 in aqueous solution at near ambient temperatures. The performance of the catalyst toward HCOOH decomposition in aqueous solution was investigated in a batch reactor at temperatures between 21 and 60 °C and HCOOH concentrations between 1.33 and 5.33 M. The apparent activation energy of the overall reaction for the production of H2 from aqueous HCOOH was determined to be 53.7 kJ/mol on the heterogeneous Pd/C catalyst. This is in good agreement with the previously reported theoretical energy barrier (∼52 kJ/mol) for H2 evolution on a Pd surface. Under the present experimental conditions, the catalyst lost activity continuously over time and the apparent deactivation energy was estimated to be 39.2 kJ/mol. Furthermore, the deactivated and spent catalyst was studied by temperature-programmed desorption experiments to reveal the possible species that caused the loss of the activity. Combining the results of our previous DFT calculations and the present experimental results, elementary steps of HCOOH decomposition on Pd in aqueous solution were proposed and discussed.

On the mechanism of the direct pathway for formic acid oxidation at a Pt(111) electrode

In order determine whether formate is a reaction intermediate of the direct pathway for formic acid oxidation at a Pt electrode, formic acid (HCOOH) oxidation at a Pt(111) electrode has been studied by normal and fast scan voltammetry in 0.1 M HClO4 solutions with different HCOOH concentrations. The relationship between the HCOOH oxidation current density (j(ox)) and formate coverage (θ(formate)) is quantitatively analyzed. The kinetic simulation reveals that the previously proposed formate pathway, with decomposition of the bridge-bonded formate (HCOO(B)) as a rate determining step (rds), cannot be the main pathway responsible for the majority of the current for HCOOH oxidation. Instead, a kinetic model based on a mechanism with formic acid adsorption [structure: see text], along with simultaneous C-H bond activation as the rds for the direct pathway, explains the measured data well. It was found for the relatively slow rate of formic acid oxidation, that adsorption-desorption of the formate is faster, which competes for the surface sites for formic acid oxidation.

Study on the Oxidation Enhancement of Formic Acid and Formate Blended Fuel Solution on Pt Catalyst

AbstractThe effect of [HCOOH]/[HCOONa] ratio on the oxidation activity of HOOH and HCOONa blended fuel solution on Pt nanocatalyst is studied using cyclic voltammetry, chronoamperometry, and Tafel analysis. Five electrolyte solutions with the same total concentrations of HCOOH and HCOONa but different [HCOOH]/[HCOONa] ratios are tested. Blended solutions containing both higher HCOOH and HCOONa concentrations are found to be more active than single HCOOH or HCOONa solution, with the solution containing 0.8 mol dm–3 HCOONa and 0.2 mol dm–3 HCOOH exhibiting the best activity. The reasons behind the better performance of the HCOOH and HCOONa blended solutions – such as electric conductivity, pH, concentrations of HCOOH, and HCOONa, ionic strength of the solution, and oxidation mechanism of HCOOH – are investigated. Enhanced oxidation activity of the HCOOH and HCOONa blended solution is observed to be the mutual effect of various reasons, with pH and [HCOO–] assuming the key roles.

PdCo supported on multiwalled carbon nanotubes as an anode catalyst in a microfluidic formic acid fuel cell

This work reports the synthesis of Pd-based alloys of Co and their evaluation as anode materials in a microfluidic formic acid fuel cell (μFAFC). The catalysts were prepared using the impregnation method followed by thermal treatment. The synthesized catalysts contain 22 wt.% Pd on multiwalled carbon nanotubes (Pd/MWCNT) and its alloys with two Co atomic percent in the sample with 4 at.% Co (PdCo1/MWCNT) and 10 at.% Co (PdCo2/MWCNT). The role of the alloying element was determined by XRD and XPS techniques. Both catalysts were evaluated as anode materials in a μFAFC operating with different concentrations of HCOOH (0.1 and 0.5 M), and the results were compared to those obtained with Pd/MWCNT. A better performance was obtained for the cell using PdCo1/MWCNT (1.75 mW cm −2) compared to Pd/MWCNT (0.85 mW cm −2) in the presence of 0.5 M HCOOH. By means of external electrode measurements, it was also possible to observe shifts in the formic acid oxidation potential due to a fuel concentration increment (ca. 0.05 V for both PdCo1/MWCNT and PdCo2/MWCNT catalysts and 0.23 V for Pd/MWCNT) that was attributed to deactivation of the catalyst material. The maximum current densities obtained were 8 mA cm −2 and 5.2 mA cm −2 for PdCo2/MWCNT and Pd/MWCNT, respectively. In this way, the addition of Co to the Pd catalyst was shown to improve the tolerance of intermediates produced during formic acid oxidation that tend to poison Pd, thus improving the catalytic activity and stability of the cell.

Carbon supported ruthenium chalcogenide as cathode catalyst in a microfluidic formic acid fuel cell

This work reports the electrochemical measurements of 20 wt.% Ru x Se y /C for oxygen reduction reaction (ORR) in presence of different concentration of HCOOH and its use as cathode catalyst in a microfluidic formic acid fuel cell ( μFAFC). The results were compared to those obtained with commercial Pt/C. Half-cell electrochemical measurements showed that the chalcogenide catalyst has a high tolerance and selectivity towards ORR in electrolytes containing up to 0.1 M HCOOH. The depolarization effect was higher on Pt/C than on Ru x Se y /C by a factor of ca. 23. Both catalysts were evaluated as cathode of a μFAFC operating with different concentrations of HCOOH. When 0.5 M HCOOH was used, maximum current densities of 11.44 mA cm −2 and 4.44 mA cm −2 were obtained when the cathode was Ru x Se y /C and Pt/C, respectively. At 0.5 M HCOOH, the peak power density of the μFAFC was similar for both catalysts, ca. 1.9 mW cm −2. At 5 M HCOOH the power density of the μFAFC using Ru x Se y , was 9.3 times higher than the obtained with Pt/C.