Recent progress in hydrogen production from formic acid decomposition

Formic acid, as the simplest carboxylic acid which can be obtained as an industrial by-product, is colorless, low toxicity, and easy to transport and storage at room temperature. Recently, Formic acid has aroused wide-spread interest as a promising material for hydrogen storage. Compared to other organic small molecules, the temperature for formic acid decomposition to produce hydrogen is lower, resulting in less CO toxicant species. Lots of catalysts on both homogeneous catalysts and heterogeneous were reported for the decomposition of formic acid to yield hydrogen and carbon dioxide at mild condition. In this paper, the recent development of mechanism and the material study for both homogeneous catalysts and heterogeneous catalysts are reviewed in detail.     

Amine-functionalized carbon nanotubes supported NiAuPd nanoparticles as an efficient in-situ prepared catalyst for formic acid dehydrogenation

Hydrogen (H₂) generation from formic acid (FA) decomposition is a promising route in practical application of hydrogen energy. As a promising H₂ supplier, besides the advantage of high H₂ content and excellent stability, FA can also be used as a mild reducing agent. Herein, an in-situ prepared NiAuPd nanoparticles (NPs) supported on amine-functionalized carbon nanotubes (NiAuPd/NH₂-CNTs) with FA as the reducing agent is successfully developed at room temperature. The as-prepared NiAuPd/NH₂-CNTs are directly used for the catalytic decomposition of FA, exhibiting excellent activity and 100% H₂ selectivity with the initial turnover frequency (TOF_initial) value of 699.1 and 3006.1 mol H₂ mol Pd^-1 h^-1 at 303 and 333 K, respectively. Moreover, the additive sodium formate (SF) can further facilitate the reduction process and enhance the catalytic performance, with the TOF_initial value of 4391.1 mol H₂ mol Pd^-1 h^-1 at 333 K, which are comparable to most of the reported heterogeneous catalysts with the complicated post-treatment. The excellent catalytic performance of NiAuPd/NH₂-CNTs is mainly attributed to the high dispersion of NPs and the boost effect of -NH₂ group on O–H cleavage. This work provides a feasible strategy to design in-situ prepared catalysts for the efficient high-quality H₂ generation from FA for fuel cells application.     

Pd nanoparticles immobilized on aniline-functionalized MXene as an effective catalyst for hydrogen production from formic acid

A simple wet chemical method was used to prepare two-dimensional transition metal carbides (MXene); PDA-MXene was prepared by alkalization of p-phenylenediamine (PDA) on MXene. And further, Pd metal nanoparticles (NPs) were conveniently loaded on the surface to catalyze the dehydrogenation of formic acid. The as-prepared Pd/PDA-MXene catalyst for the formic acid dehydrogenation was characterized by XRD, IR, TEM, and XPS. Pd-NPs with a size of about 4 nm were formed upon the PDA-MXene support surface and were well dispersed. The Pd/PDA-MXene exhibited good catalytic activity in the formic acid decomposition process without any additives, and the turnover frequency value at 50 °C was 924.4 h⁻¹, which is comparable to most of the reported noble metal catalysts under similar conditions. It is worth mentioning that the prepared catalyst maintained good catalytic activity in five consecutive catalytic cycles of the formic acid dehydrogenation experiment.     

A DFT study on production of hydrogen from biomass-derived formic acid catalyzed by Pt–TiO2

Production and storage of hydrogen from biomass component by using efficient catalysts, it can finely maintain the future energy of the world and reduce human dependence on fossil fuels. Hydrogen production mechanism via formic acid decomposition on the TiO₂ anatase (101) and Pt–TiO₂ surfaces in the solvent (water) and gaseous conditions performed by density functional theory (DFT) calculation. Regarding to the proposed routes, decomposition reaction of formic acid on TiO₂ surface incline to be followed by second route in the water which is acceptable in terms of energy. Decomposition reaction of formic acid on Pt–TiO₂ surface prefers to do it via first route (rotation around CO bond of formic acid) in solvent conditions. Furthermore, adsorption energy and geometric changes of formic acid on TiO₂ anatase (101) and Pt–TiO₂ surface in gaseous and solvent conditions were clearly studied.     

Hydrogen generation from formic acid decomposition at room temperature using a NiAuPd alloy nanocatalyst

Formic acid has been widely regarded as a safe and sustainable hydrogen storage material. Despite tremendous efforts, developing low-noble-metal-loading material with high activity for the dehydrogenation of formic acid remains a great challenge. Here, carbon supported highly homogeneous trimetallic NiAuPd alloy nanoparticles are prepared and employed as catalyst for the selective dehydrogenation of formic acid. Unexpectedly, at Ni molar contents as high as 40%, the resultant Ni_0.40Au_0.15Pd_0.45/C exhibits high activity and 100% hydrogen selectivity for hydrogen generation from formic acid aqueous solution without any additives even at 298 K. Such a low-noble-metal-loading catalyst with high activity may greatly encourage the practical application of formic acid as a hydrogen storage material.     

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.     

An effective Pd@Ni-B/C anode catalyst for electro-oxidation of formic acid

The Pd@Ni-B/C catalysts were prepared by using Ni-B/C with different amounts of Ni-B alloys as supports. The structure, morphology and element valence state of these catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The electro-catalytic performance of these catalysts for formic acid oxidation was investigated using cyclic voltammetry (CV), chronoamperometry (CA) and CO stripping experiments. It was found that an appropriate amount of Ni-B alloys plays an important role in enhancing catalytic activity and resistance to CO poisoning and improving stability of Pd based catalysts, all of which imply that Pd@Ni_1.61B_0.0199/C is promising for probable applications in direct formic acid fuel cell field.     

Au3Pd1 intermetallic compound as single atom catalyst for formic acid decomposition with highly hydrogen selectivity

Developing efficient catalysts for formic acid decomposition has been studied extensively. Herein, the Au₃Pd₁ intermetallic compound is designed as a single atom catalyst for the dehydrogenation of formic acid. By using density functional theory calculations, the thermodynamic stability, electronic structure, and reaction mechanism for the Au₃Pd₁ catalyst are systematically investigated, and the surface charge polarization and atom-ordered arrangement were confirmed to play an important role in the efficient formic acid dehydrogenation. The special positively charged Pd single atom on the Au₃Pd₁ surface becomes the adsorption site of HCOO⁻ and the reaction site for formic acid decomposition. The nearby Au sites suppress the C–O bond cleavage due to their weak interaction with CO1 and OH1. As a result, the HCOO⁻ dehydrogenation pathway is predominant on the Pd single atomic sites and the CO formation is well inhibited. This intermetallic-based catalyst can be extended to other systems and provided general guidance for efficient catalyst design.     

Engineering of the N-doped carbon support for improved performance of supported Pd catalysts in hydrogen production from gas-phase formic acid

Development of N-doped Pd/C catalysts for hydrogen production from gas-phase formic acid is a challenge. To elucidate the efficient routes of nitrogen insertion on the surface of a mesoporous carbon support, the latter was treated with melamine (Mel), dicyandiamide or NH₃ at 673 and 823 K. Pyrolysis of the melamine/carbon mixture taken in a 1:2 ratio provides an increase in the reaction rate by a factor of 5. The inserted N-sites strongly interact with Pd leading to the formation of highly dispersed Pd nanoparticles (∼1.6 nm) and active atomically dispersed Pd²⁺ species. With a further increase of the Mel/C ratio, the number of surface N-sites decreases due to occupation of carbon support pores with a g–C₃N₄–type residue. This provides a decrease in the Pd dispersion leading to lower reaction rates. Therefore, melamine is an efficient N precursor. The considered synthesis of N-doped catalysts could be scaled.     

Solvent effects on high-pressure hydrogen gas generation by dehydrogenation of formic acid using ruthenium complexes

High-pressure H₂ was produced by the selective dehydrogenation of formic acid (DFA) using ruthenium complexes at mild temperatures in various organic solvents and water. Among the solvents studied, 1,4-dioxane was the best candidate for this reaction to generate high gas pressure of 20 MPa at 80 °C using the Ru complex having a dearomatized pyridine-based pincer PN³P* ligand. This complex shows reusability for the high-pressure DFA in 1,4-dioxiane while maintaining the catalytic performance, however, deactivation occurred in other solvents. In dimethyl sulfoxide, its decomposition products may cause catalytic deactivation. The gas pressure generated in 1,4-dioxane was lower than that in water due to the high dissolution of 1,4-dioxane into CO₂ according the vapor-liquid equilibrium calculations. The role of solvent is crucial since it affected the catalytic performance and also the generated gas pressure (H₂ and CO₂) from FA.     

Hydrogen production from formic acid in fluidized bed made out of Ni-cenosphere catalyst

This research presents a method of hydrogen production from formic acid with the use of fluidized bed technology. The core-shell catalyst was developed by applying the Ni layer on cenospheres via a technique of gaseous deposition. The efficiency of the decomposition of formic acid was tested continuously in the range of 200–500 °C. An analytical method, based on infrared spectroscopy, allowing the continuous monitoring of the concentration of products in the gas phase has been developed. A 67% yield of hydrogen was achieved at 233 °C. The proposed solution in a fluidized bed has been compared with other methods of obtaining hydrogen from formic acid. The most important advantages of the proposed solutions are on-demand hydrogen generation; the use of an energy carrier that can be obtained from biomass or CO₂; simplicity of the process including easy control of the process temperature; repeatability; ease of scaling the fluidized process; the possibility of continuous monitoring of the products of the process; high efficiency of hydrogen generation per unit volume of the reactor.     

2-Dimensional metal-organic framework derived N-doped carbon immobilized Pd nanoparticles for hydrogen release from formic acid

Hydrogen release from formic acid is a significant energy supply route. However, the current catalysts suffer from low catalytic efficiency and stability. Herein, a porous N-doped carbon material with high N content (16.87%) and a large surface area (1544 m²·g^?1) were designed using a 2-dimensional metal-organic framework and etching agent potassium chloride. Due to its high N content and large surface area, ultrafine Pd particles are uniformly distributed on the porous N-doped carbon support, which effectively enhances excellent reactivity and enables a TOF value of 2365 h^?1 under additive-free conditions. The research also revealed that the strong interaction between Pd particles and pyridinic-N species can significantly slow metal agglomeration. Hence, the Pd/NC_ZIF-L (KCl) displayed good activity even after 10 cycling experiments, and it is a particularly competitive catalyst for hydrogen release from formic acid.     

Trimetallic nanoparticles: Synthesis,characterization and catalytic degradation of formic acid for hydrogen generation

PdAgFe, FePdAg and FeAgPd trimetallic nanoparticles were synthesized by seedless and step-wise simultaneous chemical reduction of Fe³⁺, Ag⁺ and Pd²⁺ by using hydrazine in presence of cetyltrimethylammonium bromide and used as a catalyst for the degradation of formic acid. The effects of nanoparticle composition, presence of sodium format (promoter), [catalyst], [formic acid] and temperature play key roles in the hydrogen generation. The Ba(OH)₂ trap experiment and water displacement technique were used to determine the generation of CO₂ and H₂, respectively. The decomposition of formic acid followed complex-order kinetics with respect to [formic acid]. It was found that FeAgPd showed a maximum catalytic activity (turn over frequency) of 75 mol H₂ per mol catalyst per h. The activation energy (E_a = 51.6 kJ/mol), activation enthalpy (ΔH = 48.9 kJ/mol) and activation entropy (ΔS = −151.0 JK^-1 mol⁻¹) were determined and discussed for the catalytic reaction. The reusability of the FeAgPd at 50 °C shows an efficient degree of activity for six consecutive catalytic cycles.     

Extracting high-purity hydrogen via sodium looping-based formic acid dehydrogenation

Formic acid (FA) has been considered as a prospective hydrogen carrier for its potentials to realize hydrogen storage, transportation, and in-situ supply under mild conditions. However, the application of FA dehydrogenation is limited by its unsatisfactory hydrogen concentration and carbon monoxide selectivity. Herein, a sodium looping-based (Na₂CO₃?NaHCO₃) formic acid dehydrogenation (SLFAD) system is proposed for high-purity hydrogen production with ultra-low CO generation via the Na₂CO₃?NaHCO₃ looping. The SLFAD system consists of three parts, which are FA dehydrogenation reactor (FADR), sorption-enhanced carbon oxide removal reactor (CORR), and sodium-based sorbent regeneration reactor (SSRR). Experimental results proved that no sodium formate and sodium oxalate was formed under NaHCO₃ reduction by H₂. A comprehensive assessment of the system was carried out to preliminary verify the feasibility and optimize the operation parameters of the SLFAD system. Results indicated that a maximum hydrogen concentration of 97.905 vol%, a minimum CO concentration of 11.97 ppm, and a high hydrogen production rate of 0.99989 kmol H₂ h^?1 can be obtained under the conditions of atmospheric pressure, FADR temperature at 80 °C, H₂O/HCOOH = 1.2, CORR temperature at 80 °C, and Na₂CO₃/HCOOH = 1.0.     

Fast hydrogen evolution by formic acid decomposition over AuPd/TiO2-NC with enhanced stability

Well-dispersed AuPd nanoparticles were immobilized on TiO₂-NC supports derived from NH₂-MIL-125(Ti) and used as highly active, stable catalysts for hydrogen production from formic acid under mild conditions. The highest total turnover frequency, i.e., 3207 h⁻¹, for formic acid dehydrogenation was achieved with Au₂Pd₈/TiO₂-NC-800 as the catalyst at 60 °C; this is 1.4 times that achieved with Au₂Pd₈/TiO₂–C-800 under the same conditions. The excellent performance of the Au₂Pd₈/TiO₂-NC-800 catalyst originates from the high anatase TiO₂ content, pyridinic N and oxygen vacancies in the support, the small size and alloying effect of the AuPd nanoparticles, and the metal–support synergistic effect. Doping the support with N improves the catalyst stability because N prevents metal particle aggregation to some extent. These results provide guidelines for the future development and applications of catalysts based on TiO₂ and metal–organic-framework-derived carbon-based materials.     

Co/multi-walled carbon nanotubes as highly efficient catalytic nanoreactor for hydrogen production from formic acid

Formic acid is well-recognized as safe and convenient hydrogen carrier. Development of active and cost-effective catalysts for formic acid to hydrogen conversion is important problem of hydrogen energy field. Herein, we report on new Co catalysts supported on oxidized multi-walled carbon nanotubes (MWCNTs), which demonstrate high efficiency in the gas-phase formic acid decomposition affording molecular hydrogen. Various parameters of the catalysts, Co loading, MWCNTs structure, and nanotubes treatment conditions, have been investigated in terms of their influence on the catalytic properties. The catalysts morphology has been characterized with a set of physicochemical methods. It is found that the catalytic activity of Co particles depends on their electronic state and location on the support. Co species located inside the MWCNTs channels are less active than Co species stabilized on the outer surface. An increase in the content of Co nanoparticles on the MWCNT outer surface leads to a higher catalytic activity.     

Formic acid dehydrogenation over PtRuBiOx/C catalyst for generation of CO-free hydrogen in a continuous-flow reactor

Liquid-phase formic acid dehydrogenation using a solid carbon supported PtRuBiO_x catalyst offers a promising and convenient method to produce CO-free hydrogen. In this study, the regenerability of the catalyst and the kinetics of formic acid dehydrogenation were investigated in a continuous-flow reactor. The kinetic experiments were carried out at temperatures between 300 and 333 K and formic acid concentrations ranging from 1.3 to 8.0 mol/L. It was found that an Arrhenius temperature dependence of the kinetic constant could represent the kinetics of formic acid dehydrogenation over the catalyst. The kinetics had first-order dependence for HCOO⁻ and half-order with respect to HCOOH under the investigated conditions. The average apparent activation energy was determined to be about 38.1 kJ/mol, which is close to the previous value (37.3 kJ/mol) obtained in a batch reactor. To gain more insight into the formic acid dehydrogenation over the catalyst, two possible mechanisms with adsorption of HCOOH or HCOO⁻ were proposed based on the experimental results and available information in literature. Two kinetic expressions were derived from the proposed reaction mechanisms. The corresponding kinetic parameters were estimated and further correlated with the apparent activation energies obtained at different formic acid concentrations.     

Bimetallic Ag-Ni nanoparticles as an effective catalyst for hydrogen generation from hydrolysis of sodium borohydride

Stable Ag-Ni bimetallic NPs was prepared, characterized, and applied for the dehydrogenation of sodium borohydride in aqueous media. The structure morphology and properties of Ag-Ni NPs were characterized by using conventional techniques such as surface field scanning electron microscopy (FESEM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV–visible spectroscopy, energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The Ag-Ni NPs were found to be highly effective catalyst to the hydrogen generation from the hydrolysis of sodium borohydride. The catalytic activity of Ag-Ni was increased with increasing the ratio of Ni (Ag₂₅-Ni₂₅ ˂ Ag₂₅-Ni₅₀ ˂ Ag₂₅-Ni₇₅). The reaction follows first-order kinetics with respect to [NaBH₄]. The apparent activation energy = 16.2 kJ/mol, activation enthalpy = 13.4 kJ/mol, and activation entropy = −135.2 J/K/mol were calculated for the hydrogen generation. The activation energy is much lower than those of the other bimetallic nano catalysts. The excellent catalytic activity, good stability, and low cost make the Ag based Ag-Ni NPs a suitable catalyst for the generation of hydrogen in sodium borohydride hydrolysis. It was found that the Ag₂₅-Ni₇₅ is one of the most reusable and durable catalyst for six consecutive cycles without any significant decrease in their catalytic activity.     

Reaction pathways derived from DFT for understanding catalytic decomposition of formic acid into hydrogen on noble metals

Formic acid decomposition on noble metals is considered to be a potential method to produce CO-free hydrogen at near ambient temperatures. However, the reaction mechanism, as well as the key points, for HCOOH decomposition on noble metals in aqueous solution remains unclear at microscopic level. In the present work, we employed density functional theory (DFT) calculation to investigate HCOOH decomposition in gas and aqueous phases on four common noble metals (Pt, Pd, Rh, and Au). Based on the present theoretical calculation results and experimental results being available in literature, two reaction pathways were proposed to understand gas- and aqueous-phase HCOOH decomposition on the noble metals. The key points that determine the activities of the metals toward HCOOH decomposition into CO₂ and H₂ in aqueous solution are clarified. Furthermore, the proposed reaction mechanism can be well extended to interpret the excellent activity of Ag–Pd core–shell bimetallic catalyst for HCOOH decomposition in aqueous solution. It is expected the present reaction mechanisms would enable us to rationally design more active heterogeneous catalysts for HCOOH decomposition into CO-free H₂ at relatively low temperatures.     

MoS2/CdS nanosheet-on-nanorod: An efficient photocatalyst for H2 generation from lactic acid decomposition

The CdS shows high selectivity on H₂ for photocatalytic lactic acid decomposition. However, the low efficiency caused by ultrafast charge recombination was not well addressed. Herein, MoS₂/CdS nanoheterostructure with intimate contact interface was synthesized in-situ and used as an efficient photocatalyst for H₂ generation. The optimum H₂ generation rate of MoS₂/CdS is 45.20 mmol g^?1 h^?1 which significantly boosts the activity of CdS (0.27 mmol g^?1 h^?1) by more than 167 folds. Band alignment of MoS₂ and CdS promoting charge transfer and separation contributes to the enhanced catalytic activity, which was well verified by multiple characterization approaches.