Highly dispersed palladium nanoparticles anchored on polyethylenimine-modified carbon nanotubes for dehydrogenation of formic acid

Formic acid has been recognized as an excellent liquid hydrogen storage material. The development of catalysts with high performance for the dehydrogenation of formic acid is significant. Herein, we employed polyethylenimine-modified carbon nanotubes as a carrier for Pd nanoparticles to synthesize a novel catalyst by a wet chemical reduction method. It was found that the amino polymers on polyethylenimine-modified carbon nanotubes have great effects on reducing the size of Pd nanoparticles, changing the electronic state of Pd, and enhancing the hydrophilicity of catalyst. Therefore, the as-synthesized Pd/CNTs-A-PEI₁₈₀₀ catalyst showed superior activity for FA dehydrogenation in the absence of additives with an initial TOF value of 1506 h^?1 and a 100% selectivity of hydrogen.     

Porous carbon supported Pd as catalysts for boosting formic acid dehydrogenation

The design of efficient catalysts is the essential to realize formic acid (FA) as a hydrogen carrier. However, it remains a challenging task. Herein, the porous carbon was prepared using ZnCo-containing zeolitic imidazole frameworks (ZIFs) as a precursor, which supported Pd as an effective catalyst for FA dehydrogenation. Porous carbon containing Co and N was synthesized by one-step method, and the Co and N promoted the activity of Pd by modifying its electron state. The catalytic performance was further improved by doping Zn into the predesigned bimetallic ZnCo-ZIFs. The addition of Zn increased the dispersion of PdCo nanoparticles, N content and specific surface area of the catalysts. When Zn/Co molar ratio was 2, the prepared catalyst (Pd/Co@CN-2) with an average diameter of PdCo about 2.6 nm exhibited the best catalytic activity, showing an initial turnover frequency value (TOF) as high as 2302 h⁻¹ even at 30 °C.     

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.     

Efficient photocatalytic hydrogen production from formic acid on inexpensive and stable phosphide/Zn3In2S6 composite photocatalysts under mild conditions

Developing an efficient, stable and low-cost photocatalytic hydrogen production from formic acid is a daunting challenge and has attracted the intense interest of many of researchers. In this paper, we report the synthesis of novel composite photocatalysts (Ni₂P/Zn₃In₂S₆ (ZIS6) and MoP/ZIS6) and their catalytic performance for H₂ production reaction from formic acid under visible light irradiation, in which Ni₂P and MoP were used as cocatalysts to enhance hydrogen generation activity of ZIS6. The photocatalytic hydrogen production rates of the optimized 1.5 wt% Ni₂P/ZIS6 (45.73 μmol·h⁻¹) and 0.25 wt% MoP/ZIS6 (92.69 μmol·h⁻¹) were 3.5 times and 7.2 times higher than that of the pure ZIS6 (12.88 μmol·h⁻¹), respectively. The apparent quantum efficiency at wavelength λ = 400 ± 10 nm for the two photocatalysts was about 1.8% and 6.4%, respectively. Significantly, it was found that the remarkable improvement of hydrogen production performance is attributed to the introduction of the phosphide cocatalysts, which can serve as a charge separation center and an active site for photocatalytic hydrogen production from the decomposition of formic acid. The reaction mechanism of photocatalytic hydrogen production from formic acid was also proposed.     

Enhanced formic acid dehydrogenation by the synergistic alloying effect of PdCo catalysts supported on graphitic carbon nitride

The catalytic ability of graphitic carbon nitride (g-C₃N₄)-supported composition-controlled PdCo catalysts towards H₂ generation from the formic acid dehydrogenation reaction was assessed in this study and a noticeable composition dependence was evidenced. It was seen that the alloying effect combined with the nitrogen functionalities present on g-C₃N₄ assisted the formation of small and well-distributed nanoparticles. This fact, combined with the electronic promotion of Pd species via charge transfer from Co and basic features of the support, resulted in enhanced catalytic activities compared to that displayed by the counterpart Pd/g-C₃N₄, reaching a TOF value of 1193 h⁻¹ for the most active catalyst among investigated (PdCo/g-C₃N₄ (1/0.7)). Furthermore, the present catalytic system showed high selectivity towards formic acid dehydrogenation, suppressing the generation of undesired CO via formic acid dehydration, which makes it a suitable candidate for practical application in fuel cells.     

Green hydrogen storage and delivery: Utilizing highly active homogeneous and heterogeneous catalysts for formic acid dehydrogenation

Significant technological revolution which allows the use of hydrogen as an efficient energy carrier and mitigates the use of fossil fuels is a crucial need of the day. Much attention has been paid to cope with the recent, reversible, and sustainable hydrogen storage technologies. Among recent strategies, formic acid (FA) has been marked as an efficient liquid chemical for hydrogen storage. The liquid organic hydrogen carriers are based on some vital characteristics that particularly reduce toxicity and consist of maximum hydrogen with efficient recyclability. This review summarizes the recent reports, studies, and investigations concerning the hydrogen production from dehydrogenation of FA, which is almost free of carbon monoxide and is considered as an excellent material in fuel cell (FC) technology. A comprehensive critical review is carried out to link the latest research progress for subsequent achievements and to investigate both the homogeneous and heterogeneous catalysts. Among these catalysts, the main focus is on precious and non-precious metals that have been progressively increased during the past decade. Furthermore, the recent developments in the generation of high-pressure hydrogen gas and its practical applications have been highlighted for better understanding.     

Bimetallic PdAu catalysts for formic acid dehydrogenation

A series of monometallic and bimetallic palladium gold catalyst were prepared and studied for the formic acid dehydrogenation reaction. Different Pd/Au compositions were employed (Pd_xAu_100-x, where x = 25; 50 and 75) and their impact on alloy structure, particle size and dispersion was evaluated. Active phase composition and reaction parameters such as temperature, formic acid concentration or formate/formic acid ratio were adjusted to obtain active and selective catalyst for hydrogen production. An important particle size effect was observed and related to Pd/Au composition for all bimetallic catalysts.     

Efficient decomposition of formic acid into hydrogen on Pd nanoparticles anchored in amine-pyridine polymer networks without extra additives at ambient condition

Palladium (Pd) is considered as the most promising catalyst for hydrogen production from formic acid decomposition (FAD), but pristine Pd catalysts are less active and readily to perform activity decay by CO poisoning. Thus the modulation of Pd is critical for its application in H₂ production from FAD. Here a Pd/APPNs catalysts by anchoring ca. 2.1 ± 0.3 nm Pd nanoparticles in the amino-pyridine polymer networks (designated as APPNs) was designed based on so-called metal-support interaction. The strong interaction between Pd and N of amine-pyridine unites was demonstrated by the X-ray photoelectron spectroscopic (XPS) analysis. It suggests the electron transfer between N and Pd, which could lower the d-band center of Pd and further effectively enhance the FAD catalysis performance. The initial FAD TOF value of 512 h^?1 and the activation energy (E_a) of ca. 22.1 kJ mol^?1 give a proper proof for the catalysis enhancement. And the third time FAD run still show a 442 h^?1 TOF, indicating an excellent catalysis stability. In addition, the production analysis by Gas chromatography (GC) show that no CO was detected. This CO-free production was also confirmed through no observation of Surface-enhanced Adsorption Infrared Spectral (SEIRAS) band at 1700-2100 cm^?1 (i.e. the CO_ad species) on Pd/ANNPs surface. This work indicates that direct modification of Pd by the functionalized support (metal-support interaction) could effective enhance the FAD catalysis performance, although further work combined with other tuning means should be push forward.     

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.     

Two-step catalytic dehydrogenation of formic acid to CO2 via formaldehyde

Formic acid has been decomposed into hydrogen and carbon dioxide through a two-step process involving the formation of formaldehyde. This allows the formation of carbon dioxide and hydrogen in two different steps, negating the need for gas separation. A novel system for the catalytic disproportionation of formic acid into formaldehyde and carbon dioxide was thus far developed using monoclinic bismuth chromate hydroxide proto-catalyst, m-Bi(OH)CrO₄. The catalytically active species, BiCrO₄, was isolated and its activity assessed for thermal disproportionation of formic acid under mild conditions (200–300 °C, tube furnace). A maximum formaldehyde production rate of 0.065 mmol/mmol catalyst/hour was observed using bismuth chromate at 250 °C. The formaldehyde produced through this method was selectively dehydrogenated to formate by an IrCl₃ catalyst at room temperature under basic conditions, with a dehydrogenation rate of 20.1 mmol of hydrogen/mmole catalyst/hour. This completes a step-by-step and yet efficient cycle of formic acid dehydrogenation.     

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.     

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.     

Cold plasma enhanced preparation of high performance PdRu/C formic acid dehydrogenation catalysts

A facile and environment-friendly atmospheric-pressure cold plasma treatment method was adopted to synthesize activated carbon supported bimetallic PdRu catalysts (PdRu/C–P) toward formic acid (FA) dehydrogenation. The results showed that the PdRu/C–P with a Pd/Ru mass ratio of 9/1 exhibited the highest activity featuring total gas volume of 337.2 ml during 4 h and initial turnover frequency (TOF) value of 954.2 h⁻¹. In comparison with the PdRu/C-T catalyst prepared by thermal reduction, enhanced FA dehydrogenation activity of the PdRu/C–P catalysts could be mainly attributed to the efficient electron transfer from Ru to active Pd in the PdRu alloy, and the high PdRu/C atomic ratios arising from the migration of the PdRu active species from the pores to the outer surface of the support affected by Coulomb repulsion effect in the plasma. The total gas volume generated by FA over the PdRu/C–P was decreased to 88.4% and 86.5% after the second and third reaction cycles, respectively, in comparison with the first cycle. However, they have been decreased to 64.6% and 64.4%, respectively, for PdRu/C-T prepared by thermal reduction. In addition, the performance of the PdRu/C–P is a little inferior to PdAu/C–P prepared by cold plasma, but its catalytic stability is much better than the expensive PdAu/C–P. The enhancement of catalytic stability for the PdRu/C–P catalyst is attributed to the small and stable particle size of PdRu, and less leaching of active species resulting from the strong metal-support interaction induced by cold plasma.     

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.     

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.     

Enhancement of visible light-driven hydrogen production over zinc cadmium sulfide nanoparticles anchored on BiVO4 nanorods

Photocatalytic water splitting to produce H₂ is a promising technology for clean energy generation. However, the use of expensive noble metals, toxicity, low charge separation efficiency and wide band gap of semiconductors hampering the widespread commercialization. Herein, we showed the potential of combining BiVO₄ nanorods with ZnCdS forming a hetero-structure which extend the spectral responsive range, separate the charge carriers effectively and enhances photocatalytic activity compared to single-component materials. The two components of hetero-structure forms an interface contact which also mitigate the problems of lower conduction band position of BiVO₄ and fast recombination of charge carriers of ZnCdS. The BiVO₄–ZnCdS hetero-structure was studied through surface morphology, crystallization properties, elemental analysis and optical properties. Under visible light irradiation, the BiVO₄–ZnCdS heterostructure produced 152.5 μmol g^?1 h^?1 hydrogen from water splitting, which was much higher than that of the individual components and stability of the hydrogen production was observed in three consecutive cycles. The as-obtained heterostructure showed improved visible light harvesting ability, prolong life of charges carriers and charge separation efficiency and Z-scheme mechanism features which results in enhanced photocatalytic activity for water splitting.     

Boron nitride supported NiCoP nanoparticles as noble metal-free catalyst for highly efficient hydrogen generation from ammonia borane

Herein, ternary metal phosphides NiCoP nanoparticles supported on porous hexagonal boron nitride (h-BN) was fabricated via hydrothermal-phosphorization strategy. The as-prepared Ni_0.8Co_1.2P@h-BN exhibited excellent catalytic performance for the hydrogen generation from ammonia borane (AB) hydrolysis, with an initial turnover frequency of 86.5 mol(H₂) mol(Ni_0.8Co_1.2P) ⁻¹ min⁻¹ at 298 K. The experimental outcome can be attributed to the synergistic effect between Ni, Co and P, as well as the strong metal-support interaction between NiCoP and h-BN. This study presents a new paradigm for supporting transition metal phosphides, and provides a new avenue to develop high performance and low cost non noble metal catalysts for hydrolysis of AB.     

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.     

Montmorillonite-hybridized g-C3N4 composite modified by NiCoP cocatalyst for efficient visible-light-driven photocatalytic hydrogen evolution by dye-sensitization

The photocatalytic hydrogen evolution performance of g-C₃N₄ was enhanced via the hybridization with montmorillonite (MMT) and using NiCoP as cocatalyst. The highest hydrogen-evolution rate from water splitting under visible-light irradiation observed over MMT/g-C₃N₄/15%NiCoP was 12.50 mmol g⁻¹ h⁻¹ under 1.0 mmol L⁻¹ of Eosin Y-sensitization at pH of 11, which was ∼26.0 and 1.6 times higher than that of MMT/g-C₃N₄ (0.48 mmol g⁻¹ h⁻¹) and g-C₃N₄/15%NiCoP (7.69 mmol g⁻¹ h⁻¹). The apparent quantum yield at 420 nm reached 40.3%. The remarkably improved photocatalytic activity can be ascribed to the increased dispersion of g-C₃N₄ layers, staggered conduction band potentials between g-C₃N₄ and NiCoP, as well as the electrostatic repulsion originated from negatively charged MMT. This work demonstrates that MMT can be an outstanding support for the deposition of catalytically active components for photocatalytic hydrogen production.     

Prickly Ni3S2 nanowires modified CdS nanoparticles for highly enhanced visible-light photocatalytic H2 production

The photocatalytic water splitting strategy is one of the most promising ways to achieve clean and renewable solar-to-hydrogen energy conversion. In this study, a highly enhanced photocatalytic H₂ production system has been achieved, using CdS nanoparticles (NPs) decorated on prickly Ni₃S₂ nanowires (NWs) as the light-driven photocatalyst. The photocatalyst was prepared by a co-precipitated method in which spiky Ni NWs were employed as starting material for prickly Ni₃S₂ NWs. Characterization analysis (XRD, TEM, XPS, etc.) show the high purity of Ni₃S₂/CdS hybrid structures and the well deposition of CdS NPs on prickly Ni₃S₂ NWs. Besides, the as synthesized Ni₃S₂/CdS photocatalyst exhibit reduced photoluminescence peak intensity, which means the Ni₃S₂ NWs functions as electron collector and transporter to quench the photoluminescence of CdS. This prickly Ni₃S₂/CdS nanocomposite demonstrates a 70 times higher H₂ production rate than that of pure CdS and a quantum efficiency of 12.3% at the wavelength of 400 nm in the absence of noble metals. This enhanced H₂ production activity is better than the one of CdS loaded with 0.5 wt% Pt. Our findings highlight the potential application of Ni₃S₂/CdS hybrid structures for visible light photocatalytic hydrogen yielding in the energy conversion field.