One-pot synthesis of PdBi/reduced graphene oxide catalyst under microwave irradiation used for formic acid electrooxidation

The Pd and PdBi nanoparticles dispersed on the reduced graphene oxide (Pd/rGO and PdBi/rGO) have been synthesized through one-pot reaction under the irradiation of microwave and the obtained composites have been characterized by transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, and their electrocatalytic activities have also been evaluated. It is found that the PdBi_0.05/rGO catalyst exhibits higher activity and better stability toward formic acid electrooxidation compared with Pd/C and Pd/rGO. The excellent electrocatalytic performance indicates that the addition of appropriate amount of Bi can greatly enhance the activity and stability of Pd catalysts for the formic acid oxidation.     

Electrooxidation of formic acid on carbon supported PtxPd1−x (x = 0-1) nanocatalysts

In this work, carbon supported Pt_xPd_1−x (x = 0-1) nanocatalysts were investigated for formic acid oxidation. These catalysts were synthesized by a surfactant-stabilized method with 3-(N,N-dimethyldodecylammonio) propanesulfonate (SB12) as the stabilizer. They show better Pt/Pd dispersion and higher catalytic performance than the corresponding commercial catalysts. Furthermore, the electrocatalytic properties of Pt_xPd_1−x/C were found to depend strongly on the Pt/Pd deposition sequence and on the Pt/Pd atomic ratio. At a lower potential, formic acid oxidation current on co-deposited Pt_xPd_1−x/C catalysts increase with increasing Pd surface concentration. Nanoscale Pd/C is a promising formic acid oxidation catalyst candidate for the direct formic acid fuel cell.     

Synthesis of Pd/C Catalyst by Modified Polyol Process for Formic Acid Electrooxidation

Pd catalyst supported on Vulcan XC‐72 carbon black was prepared by a modified polyol process. Its performance was compared with that of Pd/C catalyst prepared by impregnation reduction method by using NaBH₄ as a reducing agent for formic acid electrooxidation. Their physical characterisations were tested by means of energy dispersive analysis of X‐ray, X‐ray diffraction and transmission electron micrographs. Their activities were presented by cyclic voltammetry and chronoamperometry. The results show that the particle sizes of Pd/C catalysts prepared by modified polyol process and impregnation reduction method are 3.9 and 7.9 nm, respectively. The size dispersion of the former is narrower and more homogeneous than that of the latter. However, both of Pd/C catalysts display the characteristic diffraction peaks of a Pd face‐centred cubic (f.c.c.) crystal structure. The results of electrochemical measurements present that the Pd/C catalyst prepared by modified polyol process has the higher electrocatalytic activity and stability for formic acid electrooxidation in comparison to the Pd/C one by impregnation reduction method due to the particle size effect, and its peak current density of CV and the current of chronoamperometric curve at 1,000 s reach 33.2 and 11.2 mA cm^–2, respectively.     

Synthesis, characterization and catalytic activity of an ultrafine Pd/C catalyst for formic acid electrooxidation

An ultrafine Pd/C catalyst with a uniformly sized and highly dispersed nanostructure was synthesized by an improved liquid phase reduction method; in this process, a complexone (trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, C_yDTA) was used as an alternative stabilizer for the first time. Physicochemical characterizations indicated that the resulting Pd nanoparticles possessed ideal structural characteristics, including an average diameter of 2.1 nm, narrow size distribution ranging from 0.5 to 4.0 nm, no visible agglomerations, and no residual C_yDTA. Electrochemical tests showed that the catalytic activity of the obtained Pd/C catalyst for formic acid electrooxidation was 2.2 times greater than that of Pd/C catalyst prepared in the absence of C_yDTA. This improvement in the electrocatalytic performance was attributed to the uniformly sized and highly dispersed nanostructure, which provided a larger overall electrochemical active surface area.     

ZrC–C and ZrO2–C as Novel Supports of Pd Catalysts for Formic Acid Electrooxidation

The Pd/ZrC–C and Pd/ZrO₂–C catalysts with zirconium compounds ZrC or ZrO₂ and carbon hybrids as novel supports for direct formic acid fuel cell (DFAFC) have been synthesized by microwave‐assisted polyol process. The Pd/ZrC–C and Pd/ZrO₂–C catalysts have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), energy dispersive analysis of X‐ray (EDAX), transmission electron microscopy (TEM), and electrochemical measurements. The physical characteristics present that the zirconium compounds ZrC and ZrO₂ may promote the dispersion of Pd nanoparticles. The results of electrochemical tests show that the activity and stability of Pd/ZrC–C and Pd/ZrO₂–C catalysts show higher than that of Pd/C catalyst for formic acid electrooxidation due to anti‐corrosion property of zirconium compounds ZrC, ZrO₂, and metal–support interaction between Pd nanoparticles and ZrC, ZrO₂. The Pd/ZrC–C catalyst displays the best performance among the three catalysts. The peak current density of formic acid electrooxidation on Pd/ZrC–C electrode is nearly 1.63 times of that on Pd/C. The optimal mass ratio of ZrC to XC‐72 carbon is 1:1 in Pd/ZrC–C catalyst with narrower particle size distribution and better dispersion on surface of the mixture support, which exhibits the best activity and stability for formic acid electrooxidation among all the samples.     

Pd nanoparticles supported on carbon-modified rutile TiO2 as a highly efficient catalyst for formic acid electrooxidation

In this article, Pd nanoparticles supported on carbon-modified rutile TiO₂ (CMRT) as a highly efficient catalyst for formic acid electrooxidation were investigated. Pd/CMRT catalyst was synthesized by using liquid phase reduction method in which Pd nanoparticles was loaded on the surface of CMRT obtained through a chemical vapor deposition (CVD) process. Pd/CMRT shows three times the catalytic activity of Pd/C, as well as better catalytic stability towards formic acid electrooxidation. The enhanced catalytic property of Pd/CMRT mainly arises from the improved electronic conductivity of carbon-modified rutile TiO₂, the dilated lattice constant of Pd nanoparticles, an increasing of surface steps and kinks in the microstructure of Pd nanoparticles and slightly better tolerance to the adsorption of poisonous intermediates.     

Highly dispersed carbon-supported Pd nanoparticles catalyst synthesized by novel precipitation–reduction method for formic acid electrooxidation

The highly dispersed and ultrafine carbon-supported Pd nanoparticles (Pd/C) catalyst is synthesized by using an improved precipitation–reduction method, which involves in Pd^II → PdO·H₂O → Pd⁰ reaction path. In the method, palladium oxide hydrate (PdO·H₂O) nanoparticles (NPs) with high dispersion is obtained easily by adjusting solution pH in the presence of 1,4-butylenediphosphonic acid (H₂O₃P-(CH₂)₄-PO₃H₂, BDPA). After NaBH₄ reduction, the resulting Pd/C catalyst possesses high dispersion and small particle size. As a result, the electrochemical measurements indicate that the resulting Pd/C catalyst exhibits significantly high electrochemical active surface area and high electrocatalytic performance for formic acid electrooxidation compared with that prepared by general NaBH₄ reduction method.     

Effect of pH Value and Temperatures on Performances of Pd/C Catalysts Prepared by Modified Polyol Process for Formic Acid Electrooxidation

The highly active Pd/C catalysts for formic acid electrooxidation have been prepared by a modified polyol process at different pH values of reaction solutions and different reducing temperatures, respectively. Their physical properties have been characterised by energy dispersive analysis of X‐ray, X‐ray diffraction and transmission electron microscopy. Their electrochemical performances for formic acid electrooxidation have been tested by cyclic voltammetry and amperometric i–t curves. The results of physical characterisations show that all the Pd/C catalysts present an excellent face centered cubic crystalline structure. Their particle sizes are decreasing firstly and then increasing with the increasing of the pH values of reaction solutions. The reducing temperatures also markedly affect the Pd particle sizes. And their nanoparticles have narrow size distributions and are highly dispersed on the surface of carbon support, and Pd metal loading in Pd/C catalyst is similar to the theoretical value of 20 wt.%. The results of electrochemical measurements present that the Pd/C catalyst prepared by waterless polyol process at the pH value of 10 and the reducing temperature of 120 °C has the smallest particle size of about 5.6 nm, and exhibits the highest catalytic activity (1172.0 A · g_Pd<?h‐2.85>^–1<?h.8>) and stability for formic acid electrooxidation.     

The influence of the crystal structure of TiO2 support material on Pd catalysts for formic acid electrooxidation

The influence of the crystal structure of TiO₂ support material on Pd catalyst-mediated formic acid electrooxidation was investigated. Pd/TiO₂ catalysts were synthesized by loading Pd on TiO₂ with different crystal structures obtained by calcinations at different temperatures. Electrochemical tests showed that TiO₂ with the rutile structure improved the catalytic activity of Pd nanoparticles toward formic acid electrooxidation. Physicochemical and electrochemical characterizations revealed that the enhancement of Pd/TiO₂ (rutile) catalytic activity arose from uniform dispersion of Pd nanoparticles, an increase in surface-active sites, and good tolerance to the adsorption of poisonous intermediates (such as CO_ad, COOH_ad and so on).     

Highly Active Carbon‐supported PdSn Catalysts for Formic Acid Electrooxidation

PdSn/C catalysts with different atomic ratios of Pd to Sn were synthesised by a NaBH₄ reduction method. Electrochemical tests show that the alloy catalysts exhibit significantly higher catalytic activity and stability for formic acid electrooxidation (FAEO) than the Pd/C catalyst prepared with the same method. XRD and TEM indicate that a particle‐size effect is not the main cause for the high performance. XPS confirms that Pd is modified by Sn through an electronic effect which can decrease the adsorption strength of poisonous intermediates on Pd and thus promote the FAEO greatly.     

Preparation and characterization of core–shell structured catalysts using PtxPdy as active shell and nano-sized Ru as core for potential direct formic acid fuel cell application

Carbon-supported core–shell structured Ru@Pt_xPd_y/C catalysts with Pt_xPd_y as shell and nano-sized Ru as core are prepared by a successive reduction procedure. The catalysts are extensively characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The formic acid oxidation activity of Ru@Pt_xPd_y/C varies with the varying Pt:Pd atomic ratio. The peak oxidation potential on Ru@Pt₁Pd₂/C shifts negatively for about 200 mV compared with that of Pd/C. The higher electro-catalytic activity toward formic acid oxidation on core–shell structured Ru@Pt_xPd_y/C catalyst than that on Pt_xPd_y/C suggests the high utilization of noble metals. In addition to the enhanced noble metal utilization, Ru@Pt_xPd_y/C catalyst also shows improved stability as evidenced by chronoamperometric evaluations.     

Nanoporous PdNi/C Electrocatalyst Prepared by Dealloying High‐Ni‐content PdNi Alloy for Formic Acid Oxidation

To improve the electrochemical performance of Pd‐based catalysts for formic acid oxidation, a carbon supported nanoporous PdNi catalyst is prepared by dealloying high‐Ni‐content PdNi alloy nanoparticles in acid solution. The structure of nanoporous PdNi/C catalyst is characterized by X‐ray diffraction, transmission electron microscopy and X‐ray photoelectron spectroscopy. The electrocatalytic results show that the activity of the nanoporous PdNi/C catalyst is higher than that of nonporous Pd/C catalyst. The results demonstrate that the carbon‐supported nanoporous PdNi catalyst has a potential for application in direct formic acid fuel cells.     

Size-controlled synthesis and impedance-based mechanistic understanding of Pd/C nanoparticles for formic acid oxidation

This work provides a detailed electrochemical impedance study for formic acid electro-oxidation on size-controlled Pd/C nanoparticles, the synthesis of which was done by a simple protocol using ethylene glycol as a reducing agent. By controlling KOH concentration, this strategy provides a synthesis method for Pd nanoparticles with a selective size range of 3.9–7.5 nm. The as-prepared Pd nanoparticles exhibited size-dependent electrochemical property and electrochemical characterizations of four different Pd/C nanocatalysts (3.9, 5.2, 6.1, and 7.5 nm) showed that Pd particle with average size of 6.1 nm has the highest formic acid oxidation activity. Electrochemical impedance-based characterizations of formic acid oxidation on Pd/C suggested that at high potentials the adsorbed oxygen species could block the catalyst surface and inhibit the oxidation reaction, as reflected by the negative polarization resistance. Unlike Pd/C, the intermediate adsorbed CO species (CO_ads) plays a critical role for formic oxidation on Pt/C and thus the impedance spectra of Pd/C and Pt/C appear different potential-dependent patterns in the second quadrant. The issue of CO was investigated by an impedance investigation of Pd/C in a mixture of formic acid containing dissolved CO.     

Kinetic Study of Formic Acid Oxidation on Highly Dispersed Carbon Supported Pd–TiO2 Electrocatalyst

The highly dispersed carbon supported Pd–TiO₂ catalyst was prepared by a liquid phase reduction method with intermittent microwave irradiation. The kinetic parameters, such as the charge transfer parameter (α) and the apparent diffusion coefficient (D) of formic acid electrooxidation on a carbon supported Palladium Titanium dioxide (Pd–TiO₂/C) electrode were obtained under the quasi steady-state conditions. The dependence on temperature of the formic oxidation at a Pd–TiO₂/C electrode was also investigated and the activation energy (E _a) at different potentials was obtained.     

Phenol degradation by Fenton's process using catalytic in situ generated hydrogen peroxide

The recent reported pathway using oxygen and formic acid at ambient conditions has been utilized to generate hydrogen peroxide in situ for the degradation of phenol. An alumina supported palladium catalyst prepared via impregnation was used for this purpose. Almost full destruction of phenol was carried out within 6 h corresponding to the termination of 100 mM formic acid at the same time. In addition, a significant mineralization (60%) was attained. A simulated conventional Fenton process (CFP) using continuous addition of 300 ppm H₂O₂ displayed maximum 48% mineralization. Study of different doses of formic acid showed that decreasing the initial concentration of formic acid caused faster destruction of phenol and its toxic intermediates. The catalytic in situ generation of hydrogen peroxide system demonstrated interesting ability to oxidize phenol without the addition of Fenton's catalyst (ferrous ion). Lower Pd content catalysts (Pd1/Al and Pd0.5/Al) despite of producing higher hydrogen peroxide amount for bulk purposes, did not reach the same efficiency as the Pd5/Al catalyst in phenol degradation. The later catalyst showed a remarkable repeatability so that more than 90% phenol degradation along with 57% mineralization was attained by the used catalyst after twice recovery. Higher temperature (45 °C) gave rise to faster degradation of phenol resulting to almost the same mineralization degree as obtained at ambient temperature. Meanwhile, Pd leaching studied by atomic adsorption proved excellent stability of the catalysts.     

碳载PdCo合金催化剂对甲酸的电催化氧化

用间歇式微波法制备了不同Pt：Co原子比的碳载PdCo合金催化剂（PdCo／C）,发现在酸性溶液中Pd：Co原子比2：1催化剂对甲酸的电氧化有良好的催化活性和稳定性。从H在电极表面的吸脱附峰计算出来的结果表明,催化剂中加入一定比例的金属Co能够增加催化剂的电化学比表面。     

Formic acid electro-oxidation on carbon supported PdxPt1−x (0 ≥ x ≥ 1) nanoparticles synthesized via modified polyol method

Carbon supported nanoparticle catalysts of Pd_xPt_1−x (0 ≥ x ≥ 1) were synthesized using a modified polyol method and poly(N-vinyl-2-pyrrolidone) (PVP) as a stabilizer. Resulting nanoparticles were characterized by X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and chronoamperommetry (CA) study for formic acid electro-oxidation. Surface composition of the synthesized nanoparticles found from XPS revealed the Pt surface segregation even for the Pd-rich compositions. It is suggested that the surface segregation behavior in PdPt nanoparticles supported on carbon may be influenced, in addition to the difference in Pd and Pt surface energies, by particle size and particle interaction with the support. According to CA, the carbon supported Pd nanoparticles show the highest initial activity towards formic acid electro-oxidation at the potential of 0.3 V (RHE), due to the promotion of the direct dehydrogenation mechanism. However its stability is quite poor resulting in the fast deactivation of the Pd surface. Addition of Pt considerably improves the steady-state activity of Pd in 12 h CA experiment. CA measurements show that the most active catalyst is Pd_0.5Pt_0.5 of 4 nm size, which displays narrow size distribution and Pd to Pt surface atomic ratio of 27-73.     

载体的碱处理对Pd/C催化剂电催化性能的影响

将活性炭放入质量分数为10%的NaOH溶液中进行预处理,然后将其与未处理的活性炭分别作为载体制备Pd/C催化剂。对比两种催化剂的电化学性能发现,预处理的活性炭所制备的Pd/C催化剂,在甲酸电催化氧化活性和稳定性方面好于未处理的活性炭所制备的Pd/C催化剂。     

Effects of iron-tetrasulfophthalocyanine on the catalytic activities of Pt/C,PtRu/C,and Pd/C catalysts in a multi-anode direct formic acid fuel cell

This paper reports a systematic study of the effects of a promoter, iron-tetrasulfophthalocyanine (FeTSPc), on the catalytic activities of carbon supported Pt, PtRu, and Pd catalysts (Pt/C, PtRu/C, and Pd/C) for formic acid oxidation. A multi-anode direct formic acid fuel cell (DFAFC) was used to compare the effects on each catalyst of adding FeTSPc to the fuel stream. The FeTSPc significantly enhanced the activity of the Pt/C catalyst, but had little effect on the PtRu/C catalyst. The activity of the Pd/C catalyst was inhibited by the FeTSPc. A FeTSPc modified Pt/C was also evaluated in a conventional 5 cm² DFAFC.     

Improved electrocatalytic performance of Pd nanoparticles with size-controlled Nafion aggregates for formic acid oxidation

This work focuses on the effect of Nafion ionomer aggregation within the Pd catalytic electrode on electrocatalytic oxidation of formic acid. By a simple heat-treatment, the particle sizes of both Nafion ionomers in Nafion solution and congeries formed between Pd nanoparticles and Nafion ionomers in the catalyst ink decrease and their size distribution becomes narrow. Heat treatment of the catalyst ink leads to a significantly enhanced catalytic activity for formic acid oxidation on the Pd catalytic electrode. Such an enhancement is ascribed to the improvement in catalyst utilization verified by CO stripping voltammograms and to the decrease in charge-transfer resistance of oxidation reaction confirmed by impedance analysis. Typical XPS analysis shows that there are at least two kinds of Pd and S surface states within the catalytic electrode with the ink pre-heated at 25 °C and only one kind of Pd and S surface state at 80 °C, indicative of a better dispersion between Pd nanoparticles and smaller Nafion ionomers at a higher heat treatment temperature. Furthermore, the decrease in congeries size within the anode catalyst ink leads to a significant decrease in Nafion loading within the catalytic layer and a remarkable improvement in direct formic acid fuel cell's performance.