Preparation of Pd/ZnO/Ni hierarchical porous array film with enhanced electrocatalytic activity for methanol oxidation

In this study, we successfully synthesized a Pd/ZnO/Ni hierarchical porous array-film catalyst by electrodeposition and magnetron sputtering with the assistance of the monodisperse colloidal sphere template. Structural characterisation indicated that a layer of Pd nanoparticles was uniformly grown on the ZnO/Ni ordered bowl-like micro/nano array film. Electrochemical measurements in alkaline solution demonstrated that the as-grown array film had outstanding electrocatalytic activity for methanol oxidation. The specific activity of the Pd/ZnO/Ni porous array film was up to 130.1 mA cm⁻². The corresponding mass activity (812.7 mA mg⁻¹) was 6 times higher than that of commercial Pd/C catalyst (134.8 mA mg⁻¹), and the stability was also much better than the commercial one. These excellent electrochemical properties can be attributed to the unique hierarchical porous structure, which offers a high specific surface area for the methanol reaction, and ZnO intermediate layer, which effectively removes the poisoning species from the Pd sites through the strong oxidative hydroxyl radicals.     

PdBi alloy nanoparticle-enhanced catalytic activity toward formic acid oxidation

Improved performance and reduced costs are crucial to develop catalysts for direct formic acid fuel cells. In this study, PdBi alloy nanoparticles were synthesized using a facile seed-mediated growth method. The as-synthesized Pd₁Bi₁ alloy nanoparticles exhibited a large electrochemical surface area (46.3 m² g⁻¹) and a high mass activity (1.44 A mg⁻¹), which was 1.19- and 4.8-fold higher than that of commercial Pd/C catalysts, respectively. The PdBi alloy nanoparticle is a promising catalyst for direct formic acid fuel cells.     

Pd nanoparticles supported on MIL-101 as high-performance catalysts for catalytic hydrolysis of ammonia borane

Well dispersed ultrafine Pd NPs have been immobilized in the framework of MIL-101, and tested for the catalytic hydrolysis of ammonia borane. The powder XRD, N₂ adsorption–desorption, TEM, and ICP-AES were employed to characterize the Pd@MIL-101 catalyst. The as-synthesized Pd@MIL-101 exhibit the highest catalytic activity toward hydrolysis of AB among the Pd-based nano-catalysts ever reported, with the TOF value of 45 mol H₂ min⁻¹ (mol Pd)⁻¹.     

Pd nanoparticles on self-doping-defects mesoporous carbon supports for highly active ethanol oxidation and ethylene glycol oxidation

The high activity electrocatalysts with low cost are crucial for large-scale direct alcohol fuel cells (DAFCs) applications. In this study, the “self-doping-defects” mesoporous carbon (SDMC) as support of uniformly-dispersed Pd nanoparticles (Pd/SDMC) was prepared for high active electrooxidation by a simple route without additional surfactant and acid treatment. According to the mutually corroborated experimental and theoretical calculation results, our route can significantly increase the carbon defect, which is conducive to the anchoring and uniform distribution of Pd nanoparticles. Meanwhile, the uniquely and hierarchically mesoporous nanostructure of SDMC provides abundant pathways for mass transport in the electrooxidation reaction. Benefitting from the above advantages, Pd/SDMC exhibits superior activity than commercial Pd/C and previously reported carbon-based electrocatalysts. The mass activities and specific activities of Pd/SDMC toward ethanol oxidation reaction (EOR) are 3404.3 mA mg⁻¹, 4.48 mA cm⁻², respectively. The mass activities and specific activities of Pd/SDMC for ethylene glycol oxidation reaction (EGOR) are 4002 mA mg⁻¹, 5.26 mA cm⁻², respectively. We believe that the facile strategy to synthesis mesoporous carbon with “self-doping” defects would promote large-scale DAFCs applications in the future.     

One-step CO assisted synthesis of hierarchical porous PdRuCu nanosheets as advanced bifunctional catalysts for hydrogen evolution and glycerol oxidation

Pd-based catalysts have received wide attention due to their outstanding anti-CO poisoning property, whereas the structural instability limits their application. The hierarchical porous PdRuCu nanosheets (HP PdRuCu NSs) with large electrochemically active surface area, abundant active sites, and stable structures are synthesized through continuous access to CO bubbles. HP PdRuCu NSs exhibit excellent hydrogen evolution reaction (HER) catalytic activity with an ultralow overpotential of 25 mV at 10 mA cm^?2 and a Tafel slope of 87.5 mV dec^?1 in alkaline·media. Meanwhile, the peak mass activity and specific activity of HP PdRuCu NSs for glycerol oxidation reaction (GOR) are 1083 mA mg^?1_Pd and 38.8 A m^?2, respectively, superior to that of PdRu nanosheets (PdRu NSs), Pd nanosheets (Pd NSs), and commercial Pd black. The introduction of Ru and Cu atoms facilitates the C–C bond cleavage and the complete oxidation of glycerol to CO₂, as well as the accelerated oxidation/removal of the poisonous CO_ads in between.     

Top-down preparation of Ni–Pd–P@graphitic carbon core-shell nanostructure as a non-Pt catalyst for enhanced electrocatalytic reactions

Electrochemical reactions such as the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and methanol oxidation reaction (MOR) are essential for energy conversion applications such as water electrolysis and fuel cells. Furthermore, Pt or Ir-related materials have been extensively utilized as electrocatalysts for the OER, ORR, and MOR. To reduce the utilization of precious metals, innovative catalyst structures should be proposed. Herein, we report a bi-metallic phosphide (Ni₂P and PdP₂) structure surrounded by graphitic carbon (Ni–Pd–P/C) with an enhanced electrochemical activity as compared to conventional electrocatalysts. Despite the low Pd content of 3 at%, Ni–Pd–P/C exhibits a low overpotential of 330 mV at 10 mA cm^?2 in the OER, high specific activity (2.82 mA cm^?2 at 0.8 V) for the ORR, and a high current density of 1.101 A mg^?1 for the MOR. The superior electrochemical performance of Ni–Pd–P/C may be attributed to the synergistic effect of the bi-metallic phosphide structure and core-shell structure formed by graphitic carbon.     

Boosting hydrogen evolution activity and durability of Pd–Ni–P nanocatalyst via crystalline degree and surface chemical state modulations

Developing efficient, durable, and economical electro-catalysts for large-scale commercialization of hydrogen evolution (HER) is still challenging. Herein, we report for the first time, to the best of our knowledge, a Pd-based ternary metal phosphide as an active and stable HER catalyst. The face-centered-cubic Pd–Ni–P nanoparticles (NPs) annealed at 400 °C show the best HER activity with a low overpotential of 32 mV to realize a current density of 10 mA cm⁻² and a high mass activity of 1.23 mA μg⁻¹_Pd, superior to Pd NPs, Pd–P NPs, Pd–Ni NPs, and Pd–Ni–P NPs annealed under different temperatures. Moreover, this catalyst is also highly stable during 20 h of continuous electrolysis. Notably, the easily fabricated Pd–Ni–P NPs are among the most active Pd-based HER catalysts. This work indicates that Pd-based metal phosphides could be potentially applied as a type of practical HER catalyst and might inform the fabrication of analogous materials for hydrogen-related applications.     

Facile one-pot aqueous fabrication of interconnected ultrathin PtPbPd nanowires as advanced electrocatalysts for ethanol oxidation and oxygen reduction reactions

The catalytic features of Pt-based advanced materials closely correlate with the compositions, morphology and structure. Hence, interconnected trimetallic PtPbPd ultrathin nanowires (PtPbPd NWs) were synthesized by octylphenoxypolyethoxyethanol (NP-40)-mediated one-pot aqueous method, using in-situ generated hydrogen bubbles as the dynamic template. It is found that the types of the precursors and the amount of NP-40 are critical in this synthesis. The as-obtained architectures showed remarkable improvement in the electrocatalytic properties for ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR), surpassing those of commercial Pt/C (20 wt%), homemade PtPd NWs, PtPb NWs and PdPb NWs. Specifically, the mass activity (MA)/specific activity (SA) of PtPbPd NWs (1.20 A mg⁻¹/2.78 mA cm⁻²) is higher than those of Pt/C (0.86 A mg⁻¹/1.79 mA cm⁻²) in 0.5 M KOH solution. Furthermore, the as-synthesized catalyst displayed a positive-shift of the onset potential (E_onset, 0.993 V) for ORR over Pt/C (0.895 V) in 0.1 M KOH electrolyte. These scenarios manifest that this approach provides some new valuable guidelines for preparing novel trimetallic nanocatalysts in energy storage and conversion applications.     

A “special” anhydrous system for the preparation of alloyed Pd1Ce0.5 nanonetworks catalyst supported on carbon nanotubes with high electrochemical oxidation activity for formic acid

Herein, Pd₁Ce_0.5 alloy nanonetworks (ANNs) on multi-walled carbon nanotubes (MWCNTs) supported bimetallic catalyst (referred to Pd₁Ce_0.5/MWCNTs-D) was prepared in deep eutectic solvents (DESs). The Pd₁Ce_0.5/MWCNTs-D catalyst shows remarkable catalytic performance toward formic acid oxidation (FAO) (1968.5 mA mg_Pd^?1) and better CO anti-poisoning capability compare with Pd/MWCNTs-D, Pd/MWCNTs-W (prepared in water) and commercial Pd/C catalysts. The excellent network structure and synergistic effect are the main reasons for the improvement of electrochemical activity of Pd₁Ce_0.5/MWCNTs-D catalyst. This study provides a new method for preparation of high performance Pd-based electrocatalysts for direct formic acid fuel cell (DFAFC) applications.     

Electro-oxidation of methanol on SnO2-promoted Pd/MWCNTs catalysts in alkaline solution

The methanol electro-oxidation (MEO) on Pd–SnO₂/MWCNTs catalysts prepared by microwave-assisted polyol reduction method has been investigated. The structure, morphology and electro-catalytic performances of the catalysts were characterized with XRD, TEM and cyclic voltammetry (CV). The results showed that the highly dispersed Pd nano-particles (PdNPs) with a narrow size distribution on MWCNTs were successfully synthesized. The catalytic activity of Pd–SnO₂/MWCNTs for MEO was up to 778.8 mA/mg Pd in 0.1 M KOH solution containing 1 M methanol, which was significant higher than that of Pd/C (414.2 mA/mg Pd) or Pd–SnO₂/C (566.7 mA/mg Pd). Moreover, the MEO on Pd–SnO₂/MWCNTs electrode displayed an irreversible behavior under a diffusion control giving an exchange current density (j⁰) of 3.76 × 10⁻⁴ A cm⁻² and a Tafel slope of 149 mV dec⁻¹ (α = 0.56) at 25 °C, which indicates that Pd–SnO₂/MWCNTs catalyst has a high electro-catalytic performance for the MEO in alkaline media.     

Metal organic framework derived nitrogen-doped carbon anchored palladium nanoparticles for ambient temperature formic acid decomposition

Well-dispersed palladium nanoparticles (NPs) anchored on a porous N-doped carbon is prepared by wet chemical method, using metal organic frameworks (ZIF-8) as a precursor to derive the porous N-doped carbon support. Benefitting from the N-doping and the porous structure of the carbon materials, the final Pd NPs are in high dispersion and exhibit reduced particle sizes, with electronic structure and chemical status tuned to favor the formic acid decomposition (FAD). The prepared Pd/C_ZIF-8-950 catalysts show enhanced catalytic performance and selectivity for FAD, the turnover of frequency (TOF) and the mass activity up to 1166 h⁻¹ and 11.01 mol H₂ g⁻¹ _pd h⁻¹ were obtained at 30 °C. This work provides an effective and easy way for synthesis the Pd-based catalyst, which has enormous application prospects for the next generation hydrogen energy preparation and storage.     

Thermal and chemical activation methods applied to DFAFC anodes prepared by magnetron sputtering

Anodes consisting of Pd and bimetallic PdCu catalysts deposited directly on a carbon cloth by magnetron sputtering have been tested in a direct formic acid fuel cell. Current-voltage measurements showed that a bimetallic Pd-based catalyst temperature-treated to 300 °C exhibits the highest catalytic activity. Chemical and structural information from the surface of the catalysts was revealed by X-ray photoelectron spectroscopy (XPS) and by scanning electron microscopy (SEM). Increasing the temperature of the anode together with hydrogen peroxide (H₂O₂) treatment of the catalyst surface was proposed as an additional treatment method. In this method, the highest catalytic activity was achieved (P = 56 mW mg⁻¹) for a monometallic Pd catalyst.The enhanced catalytic efficiency after these methods had been applied was attributed to the decrease in the content of metal oxide forms, carbon-oxygen groups, and PdC_x surface contamination, where the PdC_x surface content played a major role.     

Scalable preparation of Pd/bacteria-rGO(CNT,Ketjen) composites for efficient oxygen reduction catalyst

In this paper, Pd catalysts supported on novel composite carbon supports were synthesized by the carbonization and hydrogen reduction of Pd²⁺-doped bacteria containing Ketjen EC600JD, CNT and rGO, respectively. The analysis results show that the prepared catalysts exhibit excellent ORR electrocatalytic performance in acid medium. The best ORR electrocatalytic performance was obtained for Pd/carbonized-bacteria-rGO, which exbibits a mass activity at 0.345 A mg^?1 that is 9.58 times higher than commercial Pd/C, and meanwhile displays a better stability than that of Pd/C. The enhanced performance can be attributed to nitrogen doping and flexible carbon-coating microstructure. Herein, we elaborate an efficient and ecofriendly method for the synthesis of electrocatalysts used for oxygen reduction reaction.     

Facile aqueous phase synthesis of 3D-netlike Pd–Rh nanocatalysts for methanol oxidation

The structure-activity relationship between the morphology and composition of Pd-based nanocatalysts is an important fundamental issue in direct methanol fuel cells (DMFC). Three dimensional (3D) netlike Pd–Rh bimetallic catalysts with different atomic ratios (Pd₁Rh₃, PdRh, Pd₃Rh₁) are synthesized through a simple wet chemical way using P123 as a reducing agent and KBr as morphological regulator. The morphology, structure and composition of the catalysts are proved by a series of physicochemical test technology. It is shown that the 3D-netlike structure is composed of short self-assembly nanochains. Electrochemical results display that their application towards methanol oxidation reaction (MOR) in alkaline solution. The MOR activity of the optimized Pd₃Rh₁ nanocatalyst is improved to about 4.0 mA cm⁻², which is much higher than that of the commercial Pd/C catalyst.     

Rational design of hierarchical core-shell structured CoMoO4@CoS composites on reduced graphene oxide for supercapacitors with enhanced electrochemical performance

Engineering multicomponent active materials as an advanced electrode with the rational designed core-shell structure is an effective way to enhance the electrochemical performances for supercapacitors. Herein, three-dimensional self-supported hierarchical CoMoO₄@CoS core-shell heterostructures supported on reduced graphene oxide/Ni foam have been rationally designed and prepared via a facile approach. The unique structure and the synergistic effects between two different materials, as well as excellent electronic conductivity of the reduced graphene oxide, contribute to the increased electrochemically active site and enhanced capacitance. The core-shell CoMoO₄@CoS composite displays the superior specific capacitance of 3380.3 F g⁻¹ (1 A g⁻¹) in the three-electrode system and 81.1% retention of the initial capacitance even after 6000 cycles. Moreover, an asymmetric device was successfully prepared using CoMoO₄@CoS and activated carbon as positive/negative electrodes. It is worth mentioning that the device delivered the high energy density of 59.2 W h kg⁻¹ at the power density of 799.8 W kg⁻¹ and the excellent cycle performance (about 91.5% capacitance retention over 6000 cycles). These results indicate that the core-shell CoMoO₄@CoS composites offers the novelty strategy for preparation of electrodes for energy conversion and storage devices.     

Core-shell structured ZIF-7@ZIF-67 with high electrochemical performance for all-solid-state asymmetric supercapacitor

Zeolitic imidazolate frameworks (ZIFs) are considered as a promising material for energy storage in recent years. Here, core-shell structured ZIF-7@ZIF-67 is synthesized in this work. The core-shell structured material can promote electron transfer of inner-outer metals ions of ZIF-7@ZIF-67, quicken diffusion of electrolyte ions and improve the capacitance performance compared to the ZIF-7 and ZIF-67. ZIF-7@ZIF-67 delivers good energy storage ability with a specific capacitance of 518.9 F g⁻¹ at a current density of 1 A g⁻¹ and remarkable stability with a retention of 99.6% after 4000 cycles in the three-electrode system. Furthermore, an all-solid-state asymmetric supercapacitor (ASC) device is assembled based on core-shell structured ZIF-7@ZIF-67 as positive electrode. Impressively, the ASC device displays an energy density of 31 Wh kg⁻¹ at a power density of 400 W kg⁻¹ and an excellent cyclic stability with 99.5% retention after 10,000 cycles at a current density of 10 A g⁻¹. Finally, two all-solid-state ASCs are contacted to power various lighting-emitting diodes (LED). The red LED can be kept glowing for over 10 min. These electrochemical characteristics suggest that core-shell structured ZIF-7@ZIF-67 is a potential material for energy storage device with long-life cyclic stability.     

Facile construction of 3D hyperbranched PtRh nanoassemblies: A bifunctional electrocatalyst for hydrogen evolution and polyhydric alcohol oxidation reactions

Development of highly effective and stable electrocatalysts is urgent for various energy conversion applications. Herein, a facile co-reduction approach was developed to fabricate three-dimensional (3D) hyperbranched PtRh nanoassemblies (NAs) under solvothermal conditions, where creatinine and cetyltrimethylammonium chloride (CTAC) were employed as the structure-directing agents. The as-synthesized nanocatalyst exhibited intriguing catalytic characters for hydrogen evolution reduction (HER) with a low overpotential (20 mV) at 10 mA cm⁻² and a small Tafel slope (49.01 mV dec⁻¹). Meanwhile, the catalyst showed remarkably enlarged mass activity (MA: 2.16/2.02 A mg⁻¹) and specific activity (SA: 4.16/3.88 mA cm⁻²) towards ethylene glycol and glycerol oxidation reactions (EGOR and GOR) alternative to commercial Pt black and homemade Pt₃Rh nanodendrites (NDs), PtRh₃ NDs and Pt nanoparticles (NPs). This method offers a feasible platform to fabricate bifunctional, efficient, durable and cost-effective nanocatalysts with finely engineered structures and morphologies for renewable energy devices.     

Platinum-nickel bimetallic catalyst doped with rare earth for enhancing methanol electrocatalytic oxidation reaction

Platinum (Pt) is often used as anodic catalyst for direct methanol fuel cell (DMFC). However, platinum is difficult to achieve large-scale application because of its low stability and high cost. In this work, the electrocatalytic activity and stability of the Pt-based catalyst for methanol oxidation (MOR) are significantly improved by adding Ce and Ni to the catalyst. Additionally, the rare earth element-Pr (Dy) is also chosen to be added into the catalysts for comparison. A series of PtMNi (M = Ce, Pr, Dy) catalysts are prepared by impregnation and galvanic replacement reaction methods using carbon black as support. The electrocatalytic mass activity of PtCeNi/C, PtDyNi/C, PtPrNi/C and Pt/C is 3.92, 1.86, 1.69 and 0.8 A mg_Pt⁻¹, respectively. The mass activity of these the above four catalysts after stability measurement is 3.14, 1.49, 1.27 and 0.72 A mg_Pt⁻¹. Among them, PtCeNi/C has the highest catalytic activity. These as-prepared catalysts are also characterized by various analyzing techniques, such as TEM, HRTEM, XRD, XPS, ICP-OES, STEM, STEM-EDS elemental mapping and line-scanning etc. It shows that PtCeNi/C exhibits best catalytic activity (3.92 A mg_Pt⁻¹) among the as-obtained catalysts, 4.9 times higher than that of commercial Pt/C (0.8 A mg_Pt⁻¹). PtCeNi/C is also with excellent anti-CO poisoning ability. The outstanding catalytic performance of PtCeNi/C for the MOR is mainly attributable to uniform-sized PtCeNi nanoparticles, uniform Ni, Ce and Pt element distribution, and electron interaction among Pt-, Ni- and Ce-related species (electron transferring from Pt to CeO₂).     

Synthesis of ultrafine low loading Pd–Cu alloy catalysts supported on graphene with excellent electrocatalytic performance for formic acid oxidation

Here, surfactant free composite catalysts (Pd–Cu/rGO) with Pd–Cu alloy nanoparticles uniformly distributed on graphene sheets are successfully prepared via a facile hydrothermal approach. Compared with pure Pd/rGO catalyst, the introduction of copper could dramatically enhance the performance of the catalyst in the electrocatalytic formic acid oxidation (FAO) due to the strain effect and the ligand effect. With the optimized atomic ratio of 3:1 between palladium and copper, the alloy nanoparticle shows the smallest size of 2.12 nm, thus endowing the composite catalyst with highest catalytic efficiency. With Pd load as low as 14.5%, a maximum mass current density of 1580 mA mg_Pd⁻¹, and residual current of 69.93 mA mg_Pd⁻¹ at 3000 s was achieved with our Pd₃Cu₁/rGO catalyst in the electrocatalytic FAO process.     

Pd/PdO and hydrous RuO2 difunction-modified SiO2@TaON@Ta3N5 nano-photocatalyst for efficient solar overall water splitting

A novel Pd/PdO and hydrous RuO₂ difunction-modified SiO₂@TaON@Ta₃N₅ core-shell structured nano-photocatalyst was synthesized successfully, which displayed excellent photocatalytic activity for overall water splitting into H₂ (473.52 μmol⁻¹·g⁻¹·h⁻¹), about 2.86 times higher than unmodified SiO₂@TaON@Ta₃N₅ (165.74 μmol⁻¹·g⁻¹·h⁻¹), under the visible-light irradiation with the wavelength ≥420 nm, without any sacrificial agent, as well as excellent stability against photocorrosion. The apparent quantum yield (AQY) reaches to 0.253% under irradiation intensity of 12 mW cm⁻² at 420 nm. The spatially separated Pd, PdO and RuO₂ clusters were decorated on the Ta₃N₅ surface to construct local multi-heterojunctions, which were confirmed to enhance the light absorption capability, drive efficient separation of charge carriers and directional transfer, and promote surface redox reaction kinetics of HER and OER. The trace modification of metallic Pd clusters and TaN could mainly contribute to the significant decrease in the HER overpotential, while PdO exhibited a stronger contribution than RuO₂ for OER catalytic activity. The synergetic mechanism of enhanced photocatalytic overall water splitting for hydrogen production was discussed in detail. Thus the combination of core-shell heterojunction construction and surface difunction modification provides a promising strategy for develop efficient all-in-one photocatalysts for solar overall water splitting.