Preparation of compact and porous Pd-Ni alloys and study of their performances for ethanol oxidation in alkali

Branch-Regulated Palladium-Antimony Nanoparticles Boost Ethanol Electro-oxidation to Acetate

Tuning the composition and morphology of bimetallic nanoparticles (NPs) offers an effective strategy to improve their electrocatalytic performance. In this work, we present a facile wet-chemistry procedure to engineer PdSb NPs with controlled morphology. Spherical or branched NPs are produced by tuning the heterogeneous nucleation of Sb on Pd seeds. Compared with pure Pd NPs, the incorporation of Sb not only decreases the amount of Pd used but also results in a significant increase of activity and stability for the electrocatalytic ethanol oxidation reaction (EOR). Best performances are obtained with highly branched PdSb NPs, which deliver a specific activity of 109 mA cm^-2 and a mass activity of up to 2.42 A mg_Pd^-1, well above that of a commercial Pd/C catalyst and branched Pd NPs. Moreover, PdSb displays significant stability enhancement of over 10 h for the EOR measurements. Density functional theory calculations reveal that the improved performance of PdSb NPs is related to the role played by Sb in reducing the energy barrier of the EOR rate-limiting step. Interestingly, as a side and value-added product of the EOR, acetate is obtained with 100% selectivity on PdSb catalysts.

Progress in the Development of Electrodeposited Catalysts for Direct Liquid Fuel Cell Applications

Fuel cells are a key enabling technology for the future economy, thereby providing power to portable, stationary, and transportation applications, which can be considered an important contributor towards reducing the high dependencies on fossil fuels. Electrocatalyst plays a vital role in improving the performance of the low temperature fuel cells. Noble metals (Pt, Pd) supported on carbon have shown promising performance owing to their high catalytic activity for both electroreduction and electrooxidation and have good stability. Catalyst preparation by electrodeposition is considered to be simple in terms of operation and scalability with relatively low cost to obtain high purity metal deposits. This review emphasises the role of electrodeposition as a cost-effective method for synthesising fuel cell catalysts, summarising the progress in the electrodeposited Pt and Pd catalysts for direct liquid fuel cells (DLFCs). Moreover, this review also discusses the technological advances made utilising these catalysts in the past three decades, and the factors that impede the technological advancement of the electrodeposition process are presented. The challenges and the fundamental research strategies needed to achieve the commercial potential of electrodeposition as an economical, efficient methodology for synthesising fuel cells catalysts are outlined with the necessary raw materials considering current and future savings scenario.

Cyanogel-Derived Synthesis of Porous PdFe Nanohydrangeas as Electrocatalysts for Oxygen Reduction Reaction

It is important to develop cost-efficient electrocatalysts used in the oxygen reduction reaction (ORR) for widespread applications in fuel cells. Palladium (Pd) is a promising catalyst, due to its more abundant reserves and lower price than platinum (Pt), and doping an earth-abundant 3d-transition metal M into Pd to form Pd-M bimetallic alloys may not only further reduce the use of expensive Pd but also promote the electrocatalytic performance of ORR, owing to the synergistic effect between Pd and M. Here we report a cyanogel-derived synthesis of PdFe alloys with porous nanostructure via a simple coinstantaneous reduction reaction by using K2PdIICl4/K4FeII(CN)6 cyanogel as precursor. The synthesized PdFe alloys possess hydrangea-like morphology and porous nanostructure, which are beneficial to the electrochemical performance in ORR. The onset potential of the porous PdFe nanohydrangeas is determined to be 0.988 V, which is much more positive than that of commercial Pt/C catalyst (0.976 V) and Pd black catalyst (0.964 V). Resulting from the unique structural advantages and synergetic effect between bimetals, the synthesized PdFe nanohydrangeas with porous structure have outstanding electrocatalytic activity and stability for ORR, compared with the commercial Pd black and Pt/C.

Membrane-Less Ethanol Electrooxidation over Pd-M (M: Sn, Mo and Re) Bimetallic Catalysts

The effect of the addition of three oxophilic co-metals (Sn, Mo and Re) on the electrochemical performance of Pd in the ethanol oxidation reaction (EOR) was investigated by performing half-cell and membrane-less electrolysis cell experiments. While the additions of Sn and Re were found to improve significantly the EOR performance of Pd, Mo produced no significant promotional effect. When added in significant amounts (50:50 ratio), Sn and Re produced a 3–4 fold increase in the mass-normalized oxidation peak current as compared to the monometallic Pd/C material. Both the electrochemical surface area and the onset potential also improved upon addition of Sn and Re, although this effect was more evident for Sn. Cyclic voltammetry (CV) measurements revealed a higher ability of Sn for accommodating OH- species as compared to Re, which could explain these results. Additional tests were carried out in a membrane-less electrolysis system. Pd50Re50/C and Pd50Sn50/C both showed higher activity than Pd/C in this system. Chronopotentiometric measurements at constant current were carried out to test the stability of both catalysts in the absence of a membrane. Pd50Sn50/C was significantly more stable than Pd50Re50/C, which showed a rapid increase in the potential with time. Despite operating in the absence of a membrane, both catalysts generated a high-purity (e.g., 99.99%) hydrogen stream at high intensities and low voltages. These conditions could lead to significant energy consumption savings compared to commercial water electrolyzers.

Advanced Catalytic Materials for Ethanol Oxidation in Direct Ethanol Fuel Cells

Direct ethanol fuel cells (DEFCs) have emerged as promising and advanced power systems that can considerably reduce fossil fuel dependence, and thus have attracted worldwide attention. DEFCs have many apparent merits over the analogous devices fed with hydrogen or methanol. As the key constituents, the catalysts for both cathodes and anodes usually face some problems (such as high cost, low conversion efficiency, and inferior durability) that hinder the commercialization of DEFCs. This review mainly focuses on the most recent advances in nanostructured catalysts for anode materials in DEFCS. First, we summarize the effective strategies used to achieve highly active Pt- and Pd-based catalysts for ethanol electro-oxidation, including composition control, microstructure design, and the optimization of support materials. Second, a few non-precious catalysts based on transition metals (such as Fe, Co, and Ni) are introduced. Finally, we outline the concerns and future development of anode catalysts for DEFCs. This review provides a comprehensive understanding of anode catalysts for ethanol oxidation in DEFCs.

Surface engineering of ultrasmall supported PdxBi nanoalloys with enhanced electrocatalytic activity for selective alcohol oxidation

Ultrasmall and homogeneous bimetallic PdxBi nanoalloys are well distributed on a Vulcan carbon support by a facile, low-cost synthetic strategy. The electrochemical activity of the as-prepared homogeneous PdxBi nanoalloy/carbon black nanocomposites is closely related to the content of Bi, revealing their excellent electrocatalytic performance for selective oxidation of monohydric alcohols and vicinal diols in alkali medium.