Electrochemical reduction of carbon dioxide to produce formic acid coupled with oxidative conversion of biomass

Electrochemical reduction of CO_(2)(CO_(2)RR)has become a research hot spot in recent years in the context of carbon neutrality.HCOOH is one of the most promising products obtained by electrochemical reduction of CO_(2) due to its high energy value as estimated by market price per energy unit and wide application in chemical industry.Biomass is the most abundant renewable resource in the natural world.Coupling biomass oxidative conversion with CO_(2)RR driven by renewable electricity would well achieve carbon negativity.In this work,we comprehensively reviewed the current research progress on CO_(2)RR to produce HCOOH and coupled system for conversion of biomass and its derivatives to produce value-added products.Sn-and Bi-based electrocatalysts are discussed for CO_(2)RR with regards to the structure of the catalyst and reaction mechanisms.Electro-oxidation reactions of biomass derived sugars,alcohols,furan aldehydes and even polymeric components of lignocellulose were reviewed as alternatives to replace oxygen evolution reaction(OER)in the conventional electrolysis process.It was recommended that to further improve the efficiency of the coupled system,future work should be focused on the development of more efficient and stable catalysts,careful design of the electrolytic cells for improving the mass transfer and development of environment-friendly processes for recovering the formed formate and biomass oxidation products.

Amine-functionalized hierarchically porous carbon supported Pd nanocatalysts for highly efficient H2 generation from formic acid with fast-diffusion channels

Formic acid(FA)has come to be considered a potential candidate for hydrogen storage,and the development of efficient catalysts for H2releasing is crucial for realizing the sustainable process from FA.Herein,we have developed the ultrafine Pd nanoparticle(NPs)with amine-functionalized carbon as a support,which was found to show an excellent catalytic activity in H_(2)generation from FA dehydrogenation.The synergetic mechanism between amine-group and Pd active site was demonstrated to facilitate H2generation byβ-hydride elimination.Moreover,the texture of support for Pd NPs also plays an important role in determining the reactivity of FA,since the diffusion of gaseous products makes the kinetics of diffusion as a challenge in this high performance Pd catalysts.As a result,the as-prepared Pd/NH_(2)-TPC catalyst with the small sized Pd nanoparticles and the hierarchically porous structures shows a turnover of frequency(TOF)value of 4312 h^(-1)for the additive-free FA dehydrogenation at room temperature,which is comparable to the most promising heterogeneous catalysts.Our results demonstrated that the intrinsic catalytic activities of active site as well as the porous structure of support are both important factors in determining catalytic performances in H2generation from FA dehydrogenation,which is also helpful to develop high-activity catalysts for other advanced gas-liquid-solid reactions systems.

Self-catalytic induced interstitial C-doping of Pd nanoalloys for highly selective electrocatalytic dehydrogenation of formic acid

Light-metalloid-atom-doped Pd interstitial nanoalloy is promising candidate for electrocatalysis because of the favorable electronic effect.Herein,an innovative method was developed to synthesize C-doped Pd interstitial nanoalloy using palladium acetate both as metal precursor and C dopant.Elaborate characterizations demonstrated that C atoms were successfully doped into the Pd lattice via self-catalytic decomposition of acetate ions.The as-synthesized C-doped Pd catalysts showed excellent activity and durable stability for formic acid electrooxidation.The mass activity and specific activity at 0.6 V of C-doped Pd were approximately 2.59 A/mg and 3.50 mA cm^(-2),i.e.,2.4 and 2.6 times of Pd,respectively.DFT calculations revealed that interstitial doping with C atoms induced differentiation of Pd sites.The strong noncovalent interaction between the Pd sites and the key intermediates endowed Pd with high-selectivity to direct routes and enhanced CO tolerance.This work presents a sites-differentiation strategy for metallic catalysts to improve the electrocatalysis.

Highly dispersed 1 nm Pt Pd bimetallic clusters for formic acid electrooxidation through a CO-free mechanism

Direct formic acid fuel cell(DFAFC) is an important research project in clean energy field.However,commercialization of DFAFC is still largely limited by the available catalysts with unsatisfied activity,durability and cost for formic acid electrooxidation(FAEO).Using Pt-and Pd-based nanoclusters as electrocatalysts is a particularly promising strategy to solve the above problem,but two attendant problems need to be solved firstly.(Ⅰ) The controllable synthesis of practicable and stable sub-2 nm clusters remains challenging.(Ⅱ) The catalyzing mechanism of sub-2 nm metal clusters for FAEO has not yet completely understood.Herein,different from traditional solution synthesis,by designing a novel supporting material containing electron-rich and electron-deficient functional groups,size-and dispersioncontrollable synthesis of ~1 nm PtPd nanoclusters is realized by an electrochemical process.The electrocatalytic properties and reaction mechanism of the PtPd nanoclusters for the FAEO were studied by different electrochemical techniques,in-situ fourier transform infrared(FTIR) spectra and density functional theory(DFT) calculations.The tiny PtPd nanoclusters have much higher catalytic activity and durability than commercial Pt/C,Pd/C and 3.5 nm PtPd nanoparticles.The present study shows that the metalreactant interaction plays a decisive role in determining the catalytic activity and cluster-support interaction plays a decisive role in enhancing the durability of electrocatalyst.The ratio and arrangement of Pt and Pd atoms on the surface of 1 nm PtPd cluster as well as the overall valence state,d-band center and specific surface area make them exhibit different catalytic performance and reaction mechanism from nanoparticle catalysts.In addition,in situ FTIR and DFT calculations showed that on the surface of PtPd clusters,the generation of CO_(2)through trans-COOH intermediate is the most optimal reaction pathway for the FAEO.

Ti-Fe_(2)O_(3)/Ni(OH)_(x) as an efficient and durable photoanode for the photoelectrochemical catalysis of PET plastic to formic acid

Photoelectrochemical(PEC) technology provides a promising prospect for the transformation of polyethylene terephthalate(PET) plastic wastes to produce value-added chemicals.The PEC catalytic systems with high activity,selectivity and long-term durability are required for the future up-scaling industrial applications.Herein,we employed the interfacial modification strategy to develop an efficient and stable photoanode and evaluated its PEC activity for ethylene glycol(EG,derived from PET hydrolysate) oxidation to formic acid.The interfacial modification between Fe_(2)O_(3)semiconductor and Ni(OH)xcocatalyst with ultrathin TiO_(x) interlayer not only improved the photocurrent density by accelerating the kinetics of photogenerated charge carriers,but also kept the high Faradaic efficiency(over 95% in 30 h) towards the value-added formic acid product.This work proposes an effective method to promote the PEC activity and enhance the long-term stability of photoelectrodes for upcycling PET plastic wastes.

Pt-Te alloy nanowires towards formic acid electrooxidation reaction

The high-performance anodic electrocatalysts is pivotal for realizing the commercial application of the direct formic acid fuel cells.In this work,a simple polyethyleneimine-assisted galvanic replacement reaction is applied to synthesize the high-quality PtTe alloy nanowires(PtTe NW)by using Te NW as an efficient sacrificial template.The existence of Te atoms separates the continuous Pt atoms,triggering a direct reaction pathway of formic acid electrooxidation reaction(FAEOR)at PtTe NW.The one-dimensional architecture and highly active sites have enabled PtTe NW to reveal outstanding electrocatalytic activity towards FAEOR with the mass/specific activities of 1091.25 mA mg^(-1)/45.34 A m^(-2)at 0.643 V potential,which are 44.72/23.16 and 20.26/11.75 times bigger than those of the commercial Pt and Pd nanoparticles,respectively.Density functional theory calculations reveal that Te atoms optimize the electronic structure of Pt atoms,which decreases the adsorption capacity of CO intermediate and simultaneously improves the durability of PtTe NW towards FAEOR.This work provides the valuable insights into the synthesis and design of efficient Pt-based alloy FAEOR electrocatalysts.

Interfacial engineering of holey platinum nanotubes for formic acid electrooxidation boosted water splitting

Both structure and interface engineering are highly effective strategies for enhancing the catalytic activity and selectivity of precious metal nanostructures.In this work,we develop a facile pyrolysis strategy to synthesize the high-quality holey platinum nanotubes(Pt-H-NTs)using nanorods-like Pt^(Ⅱ)-phenanthroline(PT)coordination compound as self-template and self-reduction precursor.Then,an up-bottom strategy is used to further synthesize polyallylamine(PA)modified Pt-H-NTs(Pt-HNTs@PA).PA modification sharply promotes the catalytic activity of Pt-H-NTs for the formic acid electrooxidation reaction(FAEOR)by the direct reaction pathway.Meanwhile,PA modification also elevates the catalytic activity of Pt-H-NTs for the hydrogen evolution reaction(HER)by the proton enrichment at electrolyte/electrode interface.Benefiting from the high catalytic activity of Pt-H-NTs@PA for both FAEOR and HER,a two-electrode FAEOR boosted water electrolysis system is fabricated by using Pt-H-NTs@PA as bifunctio nal electrocatalysts.Such FAEOR boosted water electrolysis system only requires the operational voltage of 0.47 V to achieve the high-purity hydrogen production,showing an energy-saving hydrogen production strategy compared to traditional water electrolysis system.

Pt-Containing Ag_2S-Noble Metal Nanocomposites as Highly Active Electrocatalysts for the Oxidation of Formic Acid

Nanocomposites with synergistic effect are of great interest for their enhanced properties in a given application. Herein, we reported the high catalytic activity of Pt-containing Ag2S-noble metal nanocomposites in formic acid oxidation, which is a key reaction in direct formic acid fuel cell. The electrochemical measurements including voltammograms and chronoamperograms are used to characterize the catalytic property of Pt-containing nanocomposites for the oxidation of formic acid. In view of the limited literatures on using nanocomposites consisting of semiconductor and noble metals for catalyzing the reactions of polymer electrolyte membrane-based fuel cells, this study provides a helpful exploration for expanding the application of semiconductor-noble metal nanocomposites.

Preparation of Ultrafine and High Dispersion Pd/C Catalyst and Its Electrocatalytic Performance for Formic Acid Oxidation

A carbon supported Pd（Pd/C） catalyst used as the anodic catalyst in the direct formic acid fuel cells（DFAFC） was prepared via the improved complex reduction method with sodium ethylenediamine tetracetate（EDTA） as stabilizer and complexing agent. This method is very simple. The average size of the Pd particles in the Pd/C catalyst prepared with the improved complex reduction method is as small as about 2.1 nm and the Pd particles in the Pd/C catalyst possess an excellent uniformity. The Pd/C catalyst shows a high electrocatalytic activity and stability for the formic acid oxidation.

Au core-PtAu alloy shell nanowires for formic acid electrolysis

Inefficient electrocatalysts and high-power consumption are two thorny problems for electrochemical hydrogen(H2)production from acidic water electrolysis.Herein we report the one-pot precise synthesis of ultrafine Au core-Pt Au alloy shell nanowires(Au@PtxAu UFNWs).Among them,Au@Pt_(0.077) Au UFNWs exhibit the best performance for formic acid oxidation reaction(FAOR)and hydrogen evolution reaction(HER),which only require applied potentials of 0.29 V and-22.6 m V to achieve a current density of 10 m A cm^(-2),respectively.The corresponding formic acid electrolyzer realizes the electrochemical H2 production at a voltage of only 0.51 V with 10 m A cm^(-2) current density.Density functional theory(DFT)calculations reveal that the Au-riched Pt Au alloy structure can facilitates the direct oxidation pathway of FAOR and consequently elevates the FAOR activity of Au@Pt_(0.077) Au UFNWs.This work provides meaningful insights into the electrochemical H_(2) production from both the construction of advanced bifunctional electrocatalysts and the replacement of OER.

Ruthenium Bisphosphine Catalyst on Functionalized Silica: Novel Efficient Catalyst for Carbon Dioxide Hydrogenation to Formic Acid

A novel efficient catalyst for the hydrogenation of carbon dioxide to formic acid ruthenium bisphosphine on functionalized silica was in situ synthesized, affording turnover frequency （TOF） of 1190 h^-1 at 100% selectivity under 80℃ with total pressure of 16.0 MPa. The catalyst can be separated from the reaction mixture easily and reused with moderate loss of activity.

Surface interaction between Pd and nitrogen derived from hyperbranched polyamide towards highly effective formic acid dehydrogenation

Hydrogen production from formic acid decomposition(FAD)is a promising means of hydrogen energy storage and utilization in fuel cells.Development of efficient catalysts for dehydrogenation of formic acid is a challenging topic.The surface chemical and electronic structure of the active catalysis components is important in formic acid decomposition at room-temperature.Here,the pyrdinic-nitrogen doped catalysts from hyperbranched polyamide were prepared via in situ polymerization reaction process by using activated carbon as a support.Because of the introduction of the polymer,the particles of the catalysts were stabilized,and the average particle diameter was only 1.64 nm.Under mild conditions,the catalysts activities were evaluated for FAD.The optimized Pd-N30/C catalyst exhibited high performance achieving almost full conversion,with a turnover frequency of 3481 h^-1 at 30℃.

Porous palladium phosphide nanotubes for formic acid electrooxidation

The development of an efficient catalyst for formic acid electrocatalytic oxidation reaction(FAEOR)is of great significance to accelerate the commercial application of direct formic acid fuel cells(DFAFC).Herein,palladium phosphide(PdxPy)porous nanotubes(PNTs)with different phosphide content(i.e.,Pd3P and Pd5P2)are prepared by combining the self-template reduction method of dimethylglyoxime-Pd(II)complex nanorods and succedent phosphating treatment.During the reduction process,the self-removal of the template and the continual inside-outside Ostwald ripening phenomenon are responsible for the generation of the one-dimensional hollow and porous architecture.On the basis of the unique synthetic procedure and structural advantages,Pd3P PNTs with optimized phos phide content show outstanding electroactivity and stability for FAEOR.Im portantly,the strong electronic effect between Pd and P promotes the direct pathway of FAEOR and inhibits the occurrence of the formic acid decomposition reaction,which effectively enhances the FAEOR electroactivity of Pd3P PNTs.In view of the facial synthesis,excellent electroactivity,high stability,and unordinary selectivity,Pd3P PNTs have the potential to be an efficient anode electrocatalyst for DFAFC.

PdNi/N-doped graphene aerogel with over wide potential activity for formic acid electrooxidation

Anti-CO poisoning ability is significant in formic acid oxidation in the fuel cell technique.Herein,Pd Ni alloy supported on N-doped graphene aerogel(Pd Ni/GA-N)was found to have catalytic ability toward formic acid electrooxidation over a wide potential range because of the improved anti-CO poisoning ability.This catalyst was fabricated by simple freeze-drying of mixture solution of graphene aerogel,polyvinylpyrrolidone,Pd^(2+)and Ni^(2+)and the subsequent thermal annealing reduction approach in the N2/H2 atmosphere.Pd-Ni alloy particles anchored over the folding N-doped graphene surface with a porous hierarchical architecture structure in the 3 D directions.It showed the catalytic performance of its maximum mass activity of 836 m A mg^(-1)in a broad potential range(0.2-0.6 V)for formic acid oxidation.The CO stripping experiment demonstrated its largely improved anti-CO poisoning ability with the peak potential of 0.67 V,approximately 60 and 40 m V less compared to those of Pd/GA-N and Pd/C samples.The high anti-CO poisoning ability and strong electronic effect resulting from the interaction between the3 D GA-N support and the Pd-Ni alloy makes it a promising catalyst for application in direct formic acid fuel cells.

Density Functional Theory Studies on the Mechanism of Activation Formic Acid Catalyzed by Transition Metal Oxide MoO

This paper systematically studies the reaction mechanisms of formic acid catalyzed by transition metal oxide MoO. Three different reaction pathways of Routes I, Ⅱ and Ⅲ were found through studying the reaction mechanism of transition metal oxide MoO catalyzing the formic acid. The transition metal oxide MoO interacts with the C=O double bond to form chiral chain compounds（Routes I and Ⅱ） and metallic compound MoOH2（Route Ⅲ）. In this paper, we have studied the mechanisms of two addition reaction pathways and hydrogen abstraction reaction pathway. Routes I and Ⅱ are both addition reactions, and their products are two different chiral compounds MoO3CH2, which are enantiomeric to each other. In Route Ⅲ, metal compounds MoOH2 and CO2 are obtained from the hydrogen abstraction reaction. Among them, the hydrogen abstraction reaction occurring in Route Ⅲ is more likely to occur than the others. By comparing the results of previous studies on the reaction of MxOy-＋ ROH（M= Mo,W; R = Me, Et）, we found that the hydrogen abstraction mechanism is completely different from the mechanism of oxygen-containing organic compound catalyzed by MxOy.

Low temperature catalytic conversion of methane to formic acid by simple vanadium compound with use of H_2O_2

Selective oxidation of methane with hydrogen peroxide was catalyzed by several simple vanadium compounds in CH3CN. The reaction could afford formic acid as the major product. Vanadyl oxysulfate （VOSO4） was found to be an efficient catalyst. Specifically, the selectivity to formic acid of 70% at a methane conversion of 6.5% could be achieved over the VOSO4 catalyst under the reaction conditions of methane pressure 3.0 MPa and temperature 333 K for 4 h. The UV-Vis spectroscopic measurements revealed that the formation of V5＋ species during the reaction might be vital for the methane activation. The reaction probably proceeded via radical mechanism.

A general strategy to the synthesis of carbon-supported PdM(M=Co,Fe and Ni)nanodendrites as high-performance electrocatalysts for formic acid oxidation

Rational synthesis of a new class of electrocatalysts with high-performance and low-cost is of great significance for future fuel cell devices. Herein, we demonstrate a general one-step simultaneous reduction method to prepare carbon-supported Pd M（M = Co, Fe, Ni） alloyed nanodendrites with the assistance of oleylamine and octadecylene. The morphology, structure and composition of the obtained Pd M nanodendrites/C catalysts have been fully characterized. The combination of the dendritic structural feature and alloyed synergy offer higher atomic utilization efficiency, excellent catalytic activity and enhanced stability for the formic acid oxidation reaction（FAOR）. Strikingly, the as-synthesized Pd Co nanodendrites/C catalyst could afford a mass current density of 2467.7 A g, which is almost 3.53 and 10.4 times higher than those of lab-made Pd/C sample(698.3 A g) and commercial Pd/C catalyst(237.6 A g), respectively. Furthermore, the PdC o nanodendrites/C catalyst also exhibit superior stability relative to the Pd/C catalysts, make it a promising anodic electrocatalyst in practical fuel cells in the future. Additionally, the present feasible synthetic approach is anticipated to provide a versatile strategy toward the preparation of other metal alloy nanodendrites/carbon nanohybrids.

The adsorption and activation of formic acid on different anatase TiO2 surfaces

Formic acid photodegradation is one of the most important reactions in organic pollution control, and helps to improve the hydrogen generation efficiency in titanium dioxide catalyzed water photodecomposition. Based on density functional theory and Reax FF molecular dynamics, the adsorption, diffusion and activation of formic acid on the different anatase TiO（101）,（001）,（010） surfaces are investigated.The result shows that the adsorption of COOH on anatase TiOsurface shrinks the energy gap between the dehydrogenation intermediate COOH and HCOO. On the anatase TiO（101） surface, the formic acid breaks the O–H bond at the first step with activation energy 0.24 eV, and the consequent break of α-H become much easier with activation energy 0.77 eV. The dissociation of α-H is the determination step of the HCOOH decomposition.

Synthesis of palladium-rhodium bimetallic nanoparticles for formic acid dehydrogenation

Herein,we report for the first time the synthesis of preformed bimetallic Pd-Rh nanoparticles with different Pd:Rh ratios(nominal molar ratio:80-20,60-40,40-60,20-80) and the corresponding Pd and Rh monometallic ones by sol immobilization using polyvinyl alcohol(PVA) as protecting agent and NaBH4 as reducing agent,using carbon nanofibers with high graphitization degree(HHT) as the desired support.The synthesized catalysts were characterized by means of Transmission Electron Microscopy(TEM) and inductively coupled plasma optical emission spectroscopy(ICP-OES).TEM shows that the average particle size of the Pd-Rh nanoparticles is the range of 3-4 nm,with the presence of few large agglomerated nanoparticles.For bimetallic catalysts,EDX-STEM analysis of individual nanoparticles demonstrated the presence of random-alloyed nanoparticles even in all cases Rh content is lower than the nominal one(calculated Pd:Rh molar ratio:90-10,69-31,49-51,40-60).The catalytic performance of the Pd-Rh catalysts was evaluated in the liquid phase dehydrogenation of formic acid to H2.It was found that Pd-Rh molar ratio strongly influences the catalytic performance.Pd-rich catalysts were more active than Rh-rich ones,with the highest activity observed for Pd90:Rh10(1792 h^(-1)),whereas Pd69:Rh31(921 h^(-1)) resulted the most stable during recycling tests.Finally,Pd90:Rh10 was chosen as a representative sample for the liquid-phase hydrogenation of muconic acid using formic acid as hydrogen donor,showing good yield to adipic acid.

Ultrafine PdAg alloy nanoparticles anchored on NH2-functionalized 2D/2D TiO_(2) nanosheet/rGO composite as efficient and reusable catalyst for hydrogen release from additive-free formic acid at room temperature

A 2 D-2 D titanium dioxide nanosheet-reduced graphene oxide(TNS-r GO)composite with better electronic conductivity and hydrophilicity was prepared by the hydrothermal method.The as-obtained TNS-r GO composite was further functionalized with 3-aminopropyltriethoxysilane(APTES)to provide a large amount of-NH2 groups on the surface for anchoring ultrafine Pd Ag alloy nanoparticles with an average particle size of 1.69 nm by a facile wet reduction approach.Benefiting from the combined effects of well-dispersed Pd Ag alloy nanoparticles,facilitated electron transfer from TNS-r GO to Pd,and increased electron density of active sites,the Pd8 Ag_(1)/NH_(2)-TNS-r GO catalyst exhibited excellent activity towards dehydrogenation of formic acid without adding any additives at 298 K,corresponding to an initial turn over frequency as high as 1090 h-1,which is much higher than that of most other state-of-theart catalysts.