Palladium-coated polyaniline nanofiber electrode as an efficient electrocatalyst for hydrogen evolution reaction

In this study, polyaniline (PANI) with abundant protonated regions was used for the first time as a palladium (Pd) support for enhanced performance in hydrogen evolution reaction (HER). For this purpose, the hierarchical Pd@PANI nanofiber electrode was easily synthesized by electrochemical polymerization of aniline on Au followed by potential-controlled electrochemical deposition of Pd nanoclusters on the PANI. The reported catalyst was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. Linear sweep voltammetry analysis was performed to evaluate the HER performance. Ion transfer behavior was investigated using electrochemical impedance spectroscopy analysis. The electrochemical tests show that the Pd@PANI/Au electrode has a low overpotential of ～60 mV at 10 mA cm^?2 and a small Tafel slope of 35 mV dec^?1 for HER in acidic media, with high catalytic activity and stability. These features will make the Pd@PANI/Au a promising candidate as a high-performance electrocatalyst for HER applications.     

One-step electroless deposition of Pd/Pt bimetallic microstructures by galvanic replacement on copper substrate and investigation of its performance for the hydrogen evolution reaction

A facile and one-step method for fabrication of Pd/Pt bimetallic microstructure using galvanic replacement reaction is presented. This electroless deposition was performed without any additive reagent via simple immersion of the copper sheet in cation aqueous solution of Pd and Pt. The as-prepared electrode was characterized by using the techniques of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and cyclic voltammetry and tested for the hydrogen evolution reaction (HER) in the acidic media. Comparison of the HER on the Pd/Pt bimetallic catalysts with different Pd:Pt percentage compositions indicated that the Pd₆₀Pt₄₀ catalyst had the highest HER activity among all the Pd/Pt catalysts and a better performance than the pure Pt. The effects of galvanic replacement time and concentration of H₂SO₄ on the catalytic activity of as-prepared electrode for HER were comparatively investigated.     

Palladium nanoparticles grown on β-Mo2C nanotubes as dual functional electrocatalysts for both oxygen reduction reaction and hydrogen evolution reaction

Developing efficient dual functional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is critical for boosting the performance of fuel cells and metal air batteries, as well as production of clean and sustainable energy source. Herein, Pd nanoparticles grown on Mo₂C nanotubes were prepared as dual functional electrocatalysts for both ORR and HER. A series of samples with different Pd loadings were fabricated, while the morphology and the structural features were well examined by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Interestingly, both the ORR activity and HER activity first increased then decreased with the increasing of Pd loading, and the sample of Mo₂C-Pd-9% exhibited the best performance among the series, superior than commercial Pd/C in both ORR and HER tests. Furthermore it also exhibited markedly higher long-term stability than Pd/C for both electrocatalytic reactions. The results may shed light on rational design of novel bi-functional electrocatalysts in the renewable energy field.     

Carbon-supported Pd nanocatalyst modified by non-metal phosphorus for the oxygen reduction reaction

A carbon-supported palladium catalyst modified by non-metal phosphorus (PdP/C) has been developed as an oxygen reduction catalyst for direct methanol fuel cells. The PdP/C catalyst was prepared by the sodium hypophosphite reduction method. The as-prepared Pd nanoparticles have a narrow size distribution with an average diameter of 2 nm. Energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) results indicate that P enters into the crystal lattice of Pd and forms an alloy. The PdP/C catalyst has an oxygen reduction reaction (ORR) activity comparable to the commercial Pt/C catalyst and a higher activity than the Pd/C catalyst synthesized by the conventional NaBH₄ reduction method. Its high catalytic activity can be attributed to its small size, lower relative crystallinity, and the formation of PdP alloy.     

DFT study of platinum and palladium overlayers on tungsten carbide: Structure and electrocatalytic activity toward hydrogen oxidation/evolution reaction

Platinum and palladium overlayers on W- and C-terminated WC(0001) surface, at coverage ranging from 0.25 ML to 2 ML, have been studied using DFT approach. Strong adhesion of metal monolayers to the WC support, accompanied by a modification of electronic structure, was evidenced. Calculated values of hydrogen binding energy on studied metal overlayers were correlated to available experimentally determined values of exchange current densities of hydrogen oxidation/evolution reaction (HOR/HER), resulting with the volcano curve with both explanatory and predictive power. None of the investigated metal/WC surfaces were found to exceed the Pt(111) surface in terms of catalytic activity toward HER/HOR. The obtained results indicate that WC may efficiently replace the precious metal support in the Pt (Pd) core–shell electrocatalyst for HER/HOR, but no synergism arising due to electronic effects of WC support was evidenced.     

Enhancement of electrocatalytic activity towards hydrogen evolution reaction by boron-modified nickel nanoparticles

Nanosized nickel particles have been synthesized by three different routes: polyol, microemulsion and precipitation/reduction methods. Nickel nanoparticles have been evaluated as electrocatalysts for the hydrogen evolution reaction (HER). The electrocatalysts have been characterized by using X-ray diffraction (XRD), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Their electrocatalytic performance in the hydrogen evolution reaction has been evaluated by means of the Tafel curves recorded in alkaline medium. The activity for the hydrogen evolution reaction increases with the increasing amount of reduced Ni in the electrocatalysts. Remarkably, the formation of a nickel-boride alloyed phase (Ni₃B) is responsible for the higher activity of the sample prepared by the precipitation/reduction method for the HER. The crystalline phase Ni₃B appears to be responsible for the very high activity in hydrogen production.     

Electrocatalytic performance of carbon dots/palladium nanoparticles composite towards hydrogen evolution reaction in acid medium

In this work, nitrogen doped carbon dots (NDCDs) and nitrogen doped carbon dots supported palladium nanoparticles composite (n-Pd@NDCDs) were synthesized through hydrothermal carbonization and thermolytic reduction using Morinda citrifolia (M. citrifolia) fruit and palladium chloride as carbon and Pd precursors, respectively. The synthesized materials viz., n-Pd@NDCDs and NDCDs were duly characterized by high resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The optical properties of NDCDs were studied by ultraviolet visible (UV–Vis), and fluorescence spectroscopy techniques. Further, the electrocatalytic hydrogen evolution reaction (HER) performance of n-Pd@NDCDs was evaluated by linear sweep voltammetry (LSV), Tafel, and electrochemical impedance spectroscopy (EIS) measurements in 0.5 M aqueous H₂SO₄. The onset potential of n-Pd@NDCDs was about −0.195 V_RHE, which was lower than NDCDS (−0.392 V_RHE) and bare glassy carbon (−0.603 V_RHE). The calculated Tafel slope values of n-Pd@NDCDs were 135 and 141.8 mV/dec, from the voltammetric and EIS methods, respectively. Moreover, the n-Pd@NDCDs exhibited small overpotential of 0.291 V to attain a current density of 10 mA/cm². The EIS studies revealed that the HER charge transfer resistance was dropped from 84.3 to 18.3 Ω/cm² while increasing of potential, which revealed good conductivity and electrocatalytic activity of n-Pd@NDCDs. Thus the present work vouched for the candidature of n-Pd@NDCDs as an effective electrocatalyst for the HER in acidic medium.     

Trash to treasure: A novel chemical route to synthesis of NiO/C for hydrogen production

Transition metal oxides (TMOs), especially nickel oxide (NiO), are environmentally benign and cost-effective materials, and have recently emerged as potential hydrogen evolution reaction (HER) electrocatalysts for future industrial scale water splitting in alkaline environment. However, their applications in HER electrocatalysts remain challenging because of poor electronic conductivity and unsatisfactory activity. Besides, the disposal of eggshell waste is also an environmentally and economically challenging problem as a result of food industry. Here, we report the synthesis of NiO nanoparticles (NPs) encapsulated in the carbonization of eggshell membrane via a green and facile approach for HER application. Noteworthy to mention here that the active carbon was made from the waste, eggshell membrane (ESM), meanwhile, the eggshell was used as a micro-reactor for preparation of electrocatalyst, NiO/C nanocomposite. Then, the as-prepared NiO/C nanocomposite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS). The SEM, EDS and TEM images reveal that NiO nanoparticles distributed on the carbon support, and XRD patterns confirm the presence of the nanoparticles are NiO and C hybrids. The catalytic activity and durability of NiO/C nanocomposite was examined for HER in 1 M KOH solution. It has been observed that NiO/C nanocomposite showed the better catalytic activity with the smallest Tafel slope of 77.8 mV dec⁻¹ than single component's result, NiO particles (112.6 mV dec⁻¹) and carbonization of ESM (94.4 mV dec⁻¹). It indicates that the HER performance of electrocatalyst can be enhanced by synergistic effect between NiO particles and carbonization of ESM, with better durability after 500 CV cycles. Furthermore, such design principle for developing interfaces between TMOs and C by a green and facile method can offer a new approach for preparing more efficient electrocatalysts.     

Robust bifunctional catalytic activities of N-doped carbon aerogel-nickel composites for electrocatalytic hydrogen evolution and hydrogenation of nitrocompounds

Nitrogen doped carbonaceous aerogel (NCA) was prepared by a simple hydrothermal treatment of cotton and ovalbumin as a carbon and nitrogen source. Magnetic Ni/NCA composite was prepared by simple chemical reduction method using hydrazine hydrate. The similar method was used in the preparation of various Ni/NCA composites with Ni percentage in the composites ranging from 45% to 75%. The magnetically active Ni/NCA catalysts so-fabricated were characterized by different analytical techniques, viz., X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive x-ray spectroscopy (EDS). The as-prepared pure Ni nanoparticles (Ni NPs) and Ni/NCA composites were employed as a prospective electrocatalysts for hydrogen evolution reaction (HER) and reduction of 4-nitrophenol. Various electrochemical parameters of Ni NPs and Ni/NCA electrocatalysts were determined and studied extensively through voltammetric and impedance methods. Electrochemical studies reveal that the prepared Ni/NCA composites show high catalytic performances and good recyclability. Particularly, Ni/NCA-60 exhibited best electrocatalytic activity among the investigated electrocatalysts in alkaline medium. Tafel slopes and constants determined for the investigated electrocatalysts revealed superior electrocatalytic performance of Ni/NCA composites over Ni NPs. From the mechanistic view point, HER likely operates through Volmer-Heyrovsky mechanism with electrochemical hydrogen adsorption as the rate determining step. Furthermore, accelerated durability test (ADT) experiments showed that Ni NPs retained about 75% of the initial activity while Ni/NCA consistently retained about 90% of the initial activity after ADT. The high catalytic activities and good durability of the Ni/NCA materials can be of potential use in the fields of electrocatalysis for hydrogen production and catalytic reduction of organic toxic pollutant.     

Efficiently catalytic transfer hydrogenation of aryl and heteroaryl halides by ultrafine palladium nanoparticles confined into UiO-66

The hydrodehalogenation of aryl and heteroaryl halides (AHHs) is very crucial for academic and industrial applications. Herein, ultrafine palladium nanoparticles (Pd NPs) with the size distribution about 1.77 ± 0.35 nm, were in-situ synthesized and confined into the metal-organic framework of UiO-66 (named as Pd@UiO-66) by impregnation reduction method without tedious post-reducing step. Pd@UiO-66 shows excellent activity with a high conversion (>90%) efficiency in the catalytic transfer hydrogenation (CTH) of AHHs under mild water systems utilizing ammonium formate as hydrogen donor. Furthermore, Pd@UiO-66 maintains highly excellent stability (conversion >95%) after 5 times reused cycles without losing catalytic activity and leaching Pd nanoparticles. This study supplies a new method for hybrid catalysts by immobilizing ultrafine Pd nanoparticles into crystalline MOFs, displaying efficient transform performance for halogen compounds by catalytic hydrogenation.     

Nitrogen doped graphene supported Pd as hydrogen evolution catalyst for electrochemical methanol reformation

Electrochemical methanol reformation (ECMR) method has been identified as one of the most effective method for on-site hydrogen production. However, concentrated research towards the development of efficient inexpensive hydrogen evolution reaction (HER) electrocatalyst holds the pivotal role in realizing the hydrogen economy. In this context, for the first time N-graphene supported Pd (Pd/NG) was synthesised and employed as an HER catalyst in ECMR process. N-graphene was synthesised by modified Hummer's method followed by Pd deposition through hydrothermal route. The electrocatalytic activity of Pd/NG for hydrogen evolution was evaluated by CV and LSV techniques. Tafel slope of Pd/NG and Pt/C was calculated from LSV curves and was found to be 33 and 31 mV/decade, respectively. Exchange current density was found to be 3.6 and 3.2 × 10⁻⁴ A cm⁻² for Pd and Pt catalysts, respectively. The enhanced electrocatalytic activity is majorly attributed to the N-doping and uniform distribution of Pd nano particles on graphene. Further, the performance of Pd/NG was also evaluated in single ECMR cell using Pt–Ru/C at anode and Pd/NG at cathode as electrocatalysts. The results indicated the suitability of Pd/NG as cathode electrocatalyst for HER in ECMR process.     

Electrocatalytic behavior of the Pd-modified electrocatalyst for hydrogen evolution

The hydrogen evolution behavior of C/CoSn, C/CoSnZn and C/CoSnZn–Pd catalysts which were prepared on a graphite substrate (C) by electrochemical deposition, as well as their electrochemical properties in the KOH solutions, have been investigated by the polarization measurements, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and electrolysis techniques. C/CoSnZn catalyst was etched in caustic to leach out zinc and to produce the Raney-type, porous electrocatalytic surface for hydrogen evolution. In order to further improve the catalytic activity of the C/CoSnZn catalyst for the hydrogen evolution reaction (HER), this catalyst was modified by loading a small amount of Pd. Results showed that the modification of C/CoSnZn catalyst by deposition of a small amount of Pd can render cathode material very active in hydrogen evolution. High catalytic activity of the C/CoSnZn–Pd catalyst depends on the surface porosity, large specific surface area and well known intrinsic catalytic activity of Pd.     

Hydrogen evolution reaction on in-plane platinum and palladium dichalcogenides via single-atom doping

Searching for the catalysts with excellent catalytic activity and high chemical stability is the key to achieve large-scale production of hydrogen (H₂) through hydrogen evolution reaction (HER). Two-dimensional (2D) platinum and palladium dichalcogenides with extraordinary electrical properties have emerged as the potential candidate for HER catalysts. Here, chemical stability, HER electrocatalytic activity, and the origin of improved HER performance of Pt/Pd-based dichalcogenides with single-atom doping (B, C, N, P, Au, Ag, Cu, Co, Fe, Ni, Zn) and vacancies are explored by first-principles calculations. The calculated defect formation energy reveals that most defective structures are thermodynamically stable. Hydrogen evolution performance on basal plane is obviously improved by single-atoms doping and vacancies. Particularly, Zn-doped and Te vacancy PtTe₂ have a ΔG_H value close to zero. Moreover, defect engineering displays a different performance on HER catalytic activity in sulfur group elements, in order of S < Te < Se in Pd-based chalcogenides, and S < Se < Te in Pt-based chalcogenides. The origin of improved hydrogen evolution performance is revealed by electronic structure and charge transfer. Our findings of the highly activating defective systems provide a theoretical basis for HER applications of platinum and palladium dichalcogenides.     

Pd nanoparticles assembled on Ni- and N-doped carbon nanotubes towards superior electrochemical activity

Metal-based catalysts within single-atom to 1–2 nm size range are attracting considerable attention recent years. Carbon-based materials with their excellent electro- and photo-chemical properties are ideal candidates as supporting substrate for constructing of metal catalyst. Here we report a palladium (less than 5 nm in average diameter) deposited Ni carbon nanotubes (CNTs) with Ni metal nanoparticles (NPs) to be around single atom to 1–2 nm on average. Mono-dispersed Pd NPs are homogeneously immobilized on both synthesized Ni- and N-doped CNTs and N-doped commercial made CNTs using poly(diallyldimethyl ammonium) chloride (PDDA) as the key bonding components. Enhanced electrocatalytic activity is observed in measurements including hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and methanol oxidation reaction (MOR), with some of the samples having higher HER (under acidic condition) and OER (under basic condition) activity comparing with the commercial Pd/C (40 wt%) sample. The result provides a forward-looking strategy for fabricating efficient and low-cost catalysts.     

Facile synthesis of well dispersed Pd nanoparticles on reduced graphene oxide for electrocatalytic oxidation of formic acid

In present study, we report a facile synthesis of crystalline, small size Pd nanoparticles (NPs) on reduced graphene oxide (RGO) abbreviated as Pd/RGO for electrocatalytic oxidation of formic acid (FA). Here, first graphene oxide (GO) was reduced by the green method using l-ascorbic acid and citric acid and further Pd NPs were decorated on RGO by a facile method without using any reducing agents. The reduction of GO to RGO and synthesis of Pd NPs was confirmed by the X-ray diffraction (XRD) and X-ray photoelectrons (XPS) techniques. Surface morphology of Pd/RGO nanocomposite was evaluated by the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The electrocatalytic behavior of Pd/RGO nanocomposite was tested by using of cyclic voltammetric (CV) technique for electro-oxidation of FA in mixed solution of 0.5 M HCOOH + 0.5 H₂SO₄ at RT. Results shows that the higher electrocatalytic activity of Pd/RGO nanocomposite compare to Pd NPs.     

Oxygen reduction reaction and hydrogen evolution reaction catalyzed by carbon-supported molybdenum-coated palladium nanocubes

Oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are two important processes for electrochemical energy storage and conversion. Herein, we describe the preparation of carbon-supported Pd nanocubes@Mo core@shell nanostructures as efficient dual catalysts for both ORR and HER. The core@shell structure was manifested by high-resolution transmission electron microscopy measurements, including high angle-angular dark field-scanning transmission electron microscopy and elemental mapping analysis. Further structural insights were obtained in X-ray diffraction and X-ray photoelectron spectroscopy measurements. The nanostructures exhibited apparent electrocatalytic activity toward both ORR and HER, and the performances were markedly higher than those without the deposition of a Mo overlayer. In ORR, the activity was even better than that of commercial Pt/C within the context of onset potential, specific and mass activities; whereas in HER, the performance of Pd nanocubes@Mo core@shell nanostructures remained subpar as compared to that of Pt/C in terms of the overpotential to reach the current density of 10 mA cm^?2, the Tafel slope was comparable and the stability was excellent. The excellent electrocatalytic performance can be attributed to the Pd-Mo synergistic effects imparted from the core-shell structure.     

High activity PtPd-WC/C electrocatalyst for hydrogen evolution reaction

Pd modified Pt over a novel support of tungsten carbide nanocrystals (the catalyst denotes as PtPd-WC/C) have been prepared by using an intermittent microwave heating (IMH) method. The as-prepared electrocatalysts are characterized by using the techniques of XRD, SEM, TEM, linear sweeping voltammetry and tested for the hydrogen evolution reaction (HER) in the acidic media. It shows a better performance for the HER on PtPd-WC/C electrocatalyst than that on Pt-WC/C electrocatalyst. In addition, these effects on the catalytic activity by changing environmental temperature and electrolyte concentration were taken into account. Kinetic study shows that the HER on the PtPd-WC/C electrocatalyst gives higher exchange current density in H₂SO₄ solution with high concentration, leading to a lower overpotential and facile kinetics. XRD, SEM and TEM images of PtPd-WC/C show the crystalline features of Pt, Pd and tungsten carbides and indicated the coexistence of these components.     

Effects of the composition on the active carbon supported Pd–Pt bimetallic catalysts for HI decomposition in the iodine–sulfur cycle

A series of binary Pd–Pt catalysts supported on active carbon were prepared by the co-impregnation and reduction method. For comparison, active carbon supported monometallic Pt and Pd catalysts were also prepared by the impregnation–reduction method. Their structure, morphology and surface area were investigated by means of X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) surface area, respectively. Their catalytic activities were evaluated for the decomposition of hydrogen iodide (HI). Furthermore, their thermal stabilities were also investigated. The results of activity tests showed that the composition of Pd–Pt binary catalysts played the important role in dictating the catalyst activity. Among the Pt, Pd and binary Pd–Pt catalysts, the 2.5%Pd–2.5%Pt/C showed the best catalytic performance for the decomposition of HI. The results of thermal stability tests showed that the binary Pd–Pt catalyst had the higher stability than the monometallic Pt and Pd catalysts.     

Fabrication of highly dispersed Pd nanoparticles supported on reduced graphene oxide for solid phase catalytic hydrogenation of 1,4-bis(phenylethynyl) benzene

In this work, nanopalladium catalysts supported on the surface of reduced graphene oxide (rGO/Pd) with different palladium loadings have been prepared by one-step reduction in aqueous phase. They were mixed with 1,4-bis(phenylethynyl)benzene (DEB) to form rGO/Pd-DEB composites according to a mass ratio of 1:3. It was shown that nanopalladium particles with particle size of about 2–6 nm were disperse uniformly on the surface of rGO when the Pd loadings were in the range of 3.97–10.60 wt%. The maximum hydrogen uptake capacity of rGO/Pd-DEB composites at 25 °C determined according to PCT method was about 182.5 ml/g after reacted with hydrogen for about 20 h, which was some lower than that of the common Pd/C-DEB pallet getter (216 ml/g) but significantly higher than alkynyl modified polyvinyl alcohol supported palladium hydrogen absorbing materials (0.32 ml/g), indicating that rGO/Pd could be used in solid phase catalytic hydrogenation due to the high dispersion of palladium nanoparticles and the physical proximity of rGO/Pd catalyst with DEB organic molecules. This provides a good potential technical way for perparing the moldable carbon aerogel hydrogen absorption materials.     

An exceptional amorphous nanoscale Pd/carbon cloth composite electrode for energy-saving oxalic acid electrolysis coupled with hydrogen production

In this paper, we report a carbon cloth/amorphous nanoscale Pd (CC/AN Pd) composite electrode and realizes the modifier-free composite of low-cost intractable carbon support and low-loading Pd metal by designing a mild and facile oxidation-ion exchange-reduction (OIR) route. This CC/AN Pd composite electrode presents high activity, robust, cost-effective, modifier-free, micro-nano porous and low Pd loading characteristics compared with the traditional Pd/C electrode. This composite electrode shows superior oxalic acid (OA) oxidization reaction (OOR) catalysis performance, outperforming all the as-reported OOR catalysts especially at high current density. Moreover, on the basis of catalysis performance and the cost of Pd loading amount, this CC/AN Pd composite electrode shows superior hydrogen evolution reaction (HER) catalysis performance with high cost-effective characteristic, surpassing all the as-reported HER catalytic electrodes. Importantly, this composite electrode was used as HER and OOR electrodes to assemble an oxalic acid electrolytic cell (OAEC), which drives 10 mA/cm² and 100 mA/cm² current density at only 1.09 V and 1.52 V voltage, respectively, and obtains up to 95.2% average faraday efficiency for 50 mA/cm² oxalic acid electrolysis. Notable, this CC/AN Pd composite electrode-based OAEC has better energy-saving and stability advantage compared with the commercial CC/Pd–C-based OAEC especially for high current density OA electrolysis. This work opens new avenues to the design of novel composite electrode materials and enables new opportunities in green energy or environmental catalysis areas.