Enhanced activity and durability of novel activated carbon-supported PdSn heat-treated cathode catalyst for polymer electrolyte fuel cells

Enhanced durability of Pd/CeO2-C via metal-support interaction for oxygen reduction reaction

It is a challenge to improve the long-term durability of Pd-based electrocatalysts for oxygen reduction reaction (ORR) in fuel cells. Herein, Pd/CeO2-C-T (T= 800 °C, 900 °C and 1000 °C) hybrid catalysts with metal-support interaction are prepared from Ce-based metal organic framework precursor. Abundant tiny CeO2nanoclusters are produced to form nanorod structures with uniformly distributed carbon through a calcination process. Meanwhile, both carbon and CeO2nanoclusters have good contact with the following deposited surfactant-free Pd nanoclusters. Benefited from the large specific surface area, good conductivity and structure integrity, Pd/CeO2-C-900 exhibits the best electrocatalytic ORR performance: onset potential of 0.968 V and half-wave potential of 0.857 V, outperforming those obtained on Pd/C counterpart. In addition, the half-wave potential only shifts 7 mV after 6000 cycles of accelerated durability testing, demonstrating robust durability.

Interfacial oxygen atom modification of a PdSn alloy to boost oxygen reduction in zinc-air batteries

Modifying the surface of a catalyst with heteroatoms can regulate the interfacial atomic valence state and adjust the charge distribution, which is promising for obtaining desirable platinum carbon catalyst (Pt/C)-matched oxygen reduction reaction (ORR) catalytic performance. Here, we developed an efficient method to access O-rich crystalline interfacial-exposed palladium-tin alloy (111) crystal surfaces [Pd3Sn (111)] for highly efficient ORR via direct reduction of Pd/Sn metal salt species that are well dispersed in a nitrogen, phosphorus-doped carbonaceous (NPC) substrate. In addition to the other materials, preembedded Pd/Sn metal salt species in NPC control the release of metal sources upon reduction in the liquid phase, resulting in the grafting of an as-prepared PdSn alloy with many merits, such as efficient electron conduction, short-range crystallinity and increased crystal interface exposure. The presence of a considerable quantity of oxygen atoms at the interface of small-sized PdSn alloys on NPC substrates has been methodically verified by powder X-ray diffraction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy characterizations. The PdSn-O sample exhibited excellent ORR activity, achieving an onset potential of ∼0.99 V and a half-wave potential of ∼0.88 V at 1600 rpm in O2-saturated 1.0 M KOH. Density functional theory simulations of pure Pd, Pd-O, the PdSn alloy and PdSn-O suggest that interfacial oxygen atom modification is responsible for the significantly improved ORR activity. The assembled zinc-air battery provides a high specific power of 218.9 mW cm-2 and a specific capacity of 810.6 mAh gZn-1. Our approach has the potential to stimulate the preparation of O-rich crystalline interfacial-exposed alloy compounds for other energy conversion applications.

Valorisation of spent tire rubber as carbon adsorbents for Pb(II) and W(VI) in the framework of a Circular Economy

Spent tire rubber-derived chars and their corresponding H3PO4 and CO2-activated chars were used as adsorbents in the recovery of Pb(II) ion and (W(VI)) oxyanion from synthetic solutions. The developed chars (both raw and activated) were thoroughly characterized to have insight about their textural and surface chemistry properties. H3PO4-activated chars presented lower surface areas than the raw chars and an acidic surface chemistry which affected the performance of these samples as they showed the lowest removals of the metallic ions. On the other hand, CO2-activated chars presented increased surface areas and increased mineral content compared to the raw chars, having presented higher uptake capacities for both Pb(II) (103-116 mg/g) and W(VI) (27-31 mg/g) ions. Cation exchange with Ca, Mg and Zn ions was appointed as a mechanism for Pb removal, as well as surface precipitation in the form of hydrocerussite (Pb3(CO3)2(OH)2). W(VI) adsorption might have been ruled by strong electrostatic attractions between the negatively charged tungstate species and the highly positively charged carbons' surface.The results shown in this work allow concluding that the valorisation of spent tire rubber through pyrolysis and the subsequent activation of the obtained chars is an alternative and a feasible option to generate adsorbent materials with a high uptake capacity of critical metallic elements.

Oxygen-rich PdSnCu nanocrystals with particle connection features as enhanced catalysts for ethanol oxidation reaction

Most electrocatalysts show a high mass and special activity during the ethanol oxidation reaction, but those still suffer from limited stability, finite renewable capability and poor anti-poisoning durability. Furthermore, the reliable structure and appropriate composition of catalysts are fairly associated with the electrocatalysis performance. Herein, we report the development of trimetallic Pd₆₁Sn₃₄Cu₅nanocrystals (NCs) whose rough surfaces are rich in step atoms and coupled with abundant of SnO_xand CuO, which may effectively boost reaction activity and rapidly remove carbonaceous intermediate, respectively. Under the tuning on the composition, the defect rich Pd₆₁Sn₃₄Cu₅NCs exhibit elevated electrocatalysis activity and durability for ethanol oxidation reaction with an optimized mass activity (1.26 AmgPd-1) and specific activity (10.6 mA cm^-2), which is about 2.21 and 2.58 times greater than that of the commercial Pd/C catalyst (0.57 AmgPd-1and 4.1 mA cm^-2).

High Active PdSn Binary Alloyed Catalysts Supported on B and N Codoped Graphene for Formic Acid Electro-Oxidation

A series of PdSn binary catalysts with varied molar ratios of Pd to Sn are synthesized on B and N dual-doped graphene supporting materials. The catalysts are characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). Formic acid electro-oxidation reaction is performed on these catalysts, and the results reveal that the optimal proportion of Pd:Sn is 3:1. X-ray photoelectron spectroscopy (XPS) measurements show that when compared with 3Pd1Sn/graphene, B and N co-doping into the graphene sheet can tune the electronic structure of graphene, favoring the formation of small-sized metallic nanoparticles with good dispersion. On the other hand, when compared with the monometallic counterparts, the incorporation of Sn can generate oxygenated species that help to remove the intermediates, exposing more active Pd sites. Moreover, the electrochemical tests illustrate that 3Pd1Sn/BN-G catalyst with a moderate amount of Sn exhibits the best catalytic activity and stability on formic acid electro-oxidation, owing to the synergistic effect of the Sn doping and the B, N co-doping graphene substrate.

Preparation of Nanoporous PdIrZn Alloy Catalyst by Dissolving Excess ZnO for Cathode of High- Temperature Polymer Electrolyte Membrane Fuel Cells

Carbon-supported nanoporous palladium-iridium–zinc (NP-PdIrZn) electrocatalyst was prepared through the modification of the alcohol-reduction process following the selective dissolution of excess ZnO nanoparticles using NaOH solution. The electrocatalyst was applied successfully to the cathode for a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC). X-ray diffraction (XRD) patterns of the NP-PdIrZn nanoparticles suggests formation of the ternary alloy and complete removal of ZnO without the formation of individual Pd, Ir, or Zn nanoparticles. Moreover, transmission electron microscopy (TEM) images displayed porous nanoparticles with an irregular shape, which was generated by removing the ZnO from the PdIrZn–ZnO nanocomposites, and was prepared by using the excessive Zn precursor. The electrochemical surface area (ECSA) of the NP-PdIrZn catalysts was estimated by cyclic voltammetry using a rotating disk electrode method , and the oxygen reduction reaction (ORR) activity was evaluated by a linear sweep method. The NP-PdIrZn catalysts showed larger ECSA and higher ORR activity than those of the PdIr and PdIrZn catalysts, which may be attributed to the increased exposed surface area by selective etching of the ZnO in the composites. Furthermore, the NP-PdIrZn catalyst exhibited excellent performance (0.66 V) in a single cell under the HT-PEMFC condition than those of the PdIr (0.58 V) and PdIrZn (0.62 V) catalysts, indicating that geometric and electronic control of Pd-based alloy can improve the single-cell performance for the HT-PEMFC.