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

Facile pyrolysis synthesis of abundant FeCo dual-single atoms anchored on N-doped carbon nanocages for synergistically boosting oxygen reduction reaction

Single-atom transition metal-based nitrogen-doped carbon (M-Nx-C) is regarded as high-efficiency and cost-effectiveness alternatives to replace noble metal catalysts for oxygen reduction reaction (ORR) in renewable energy storage and conversion devices. In this work, rich FeCo dual-single atoms were efficiently entrapped into N-doped carbon nanocages (FeCo DSAs-NCCs) by simple pyrolysis of the bimetallic precursors doped zeolitic imidazolate framework-8 (ZIF-8), as affirmed by a series of characterizations. The graphitization degree of the N-doping carbon substrate was regulated by modulating the pyrolysis temperature and the types of the metal salts. The typical catalyst substantially improved the alkaline ORR performance, with the onset potential (Eonset) of 0.99 V (vs. RHE) and half-wave potential (E1/2) of 0.88 V (vs. RHE). Ultimately, the catalyst-assembled Zn-air battery possessed a higher open-circuit voltage of 1.501 V, larger power density of 123.7 mW cm-2, and outstanding durability for 150 h. This study provides a guide on developing ORR catalysts for electrochemical energy conversion and storage technology.

Alloying Iron into Palladium Nanoparticles for an Efficient Catalyst in Acetylene Dicarbonylation

Motivated by the prominent catalytic performance and durability of nanoalloy catalysts, the Pd-based bimetallic nanoalloy catalysts were prepared using an aqueous reduction method. The Fe-Pd bimetallic nanoalloy catalyst (nano-Fe/Pd) demonstrated 98.4% yield and 99.7% selectivity for the unsaturated 1,4-dicarboxylic acid diesters. Moreover, the inductively coupled plasma (ICP) analysis shows that the Pd leaching of the catalyst can be effectively suppressed by alloying Fe atoms into the Pd crystal lattice for acetylene dicarbonylation. The detailed catalyst structure and morphology characterization demonstrate that introducing Fe into the Pd nanoparticles tunes the electronic-geometrical properties of the catalyst. Theoretical calculations indicate that the electrons of Fe transfer to Pd in the nano-Fe/Pd catalyst, enhancing activation of the C≡C bond in acetylene and weakening CO absorption capacity on catalyst surfaces. Alloying Fe into the Pd nanocatalyst effectively inhibits active metal leaching and improves catalyst activity and stability under high-pressure CO reactions.

Cyanogel-Induced Synthesis of RuPd Alloy Networks for High-Efficiency Formic Acid Oxidation

For direct formic acid fuel cells (DFAFC), palladium (Pd)-based alloy catalysts with competitive morphology and elemental composition are essential to boost the performance of the formic acid oxidation reaction (FAOR) in the anode zone. Herein, we design and synthesize RuPdx alloy nano-network structures (ANs) via the facile wet-chemical reduction of Pd-Ru cyanogel (Pdx [Ru(CN)6]y·aH2O) as an effective electrocatalyst for the FAOR. The formation of Pd-Ru cyanogel depends on the facile coordination of K2PdCl4 and K3 [Ru(CN)6]. The unique structure of cyanogel ensures the presentation of a three-dimensional mesoporous morphology and the homogeneity of the elemental components. The as-prepared RuPd3 ANs exhibit good electrocatalytic activity and stability for the FAOR. Notably, the RuPd3 ANs achieve a mass-specific activity of 2068.4 mA mg−1 in FAOR, which shows an improvement of approximately 16.9 times compared to Pd black. Such a competitive FAOR performance of RuPd3 ANs can be attributed to the advantages of structure and composition, which facilitate the exposure of more active sites, accelerate mass/electron transfer rates, and promote gas escape from the catalyst layer, as well as enhance chemical stability.

Ordered intermetallic compounds combining precious metals and transition metals for electrocatalysis

Ordered intermetallic alloys with significantly improved activity and stability have attracted extensive attention as advanced electrocatalysts for reactions in polymer electrolyte membrane fuel cells (PEMFCs). Here, recent advances in tuning intermetallic Pt- and Pd-based nanocrystals with tunable morphology and structure in PEMFCs to catalyze the cathodic reduction of oxygen and the anodic oxidation of fuels are highlighted. The fabrication/tuning of ordered noble metal-transition metal-bonded intermetallic PtM and PdM (M = Fe, Co) nanocrystals by using high temperature annealing treatments to promote the activity and stability of electrocatalytic reactions are discussed. Furthermore, the further improvement of the efficiency of this unique ordered intermetallic alloys for electrocatalysis are also proposed and discussed. This report aims to demonstrate the potential of the ordered intermetallic strategy of noble and transition metals to facilitate electrocatalysis and facilitate more research efforts in this field.

Synthesis of Co/CeO2 hetero-particles with abundant oxygen-vacancies supported by carbon aerogels for ORR and OER

It is highly significant for the fabrication of rechargeable metal-air batteries to develop cost-efficient and high-performance electrocatalysts of bifunctionality for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, we demonstrate a hybrid composed of CeO₂-decorated Co nanoparticles supported on three-dimensionally porous carbon aerogels (Co-CeO₂/C aerogels) as a superior bifunctional electrocatalyst. The preparation of Co-CeO₂/C aerogels depends on the formation of a novel CeCl₃/K₃Co(CN)₆-chitosan (CS) hydrogel, during which the cyanide groups of K₃Co(CN)₆ combines the hydroxyls in CS by hydrogen bridges, accompanying with the substitution of chloride groups in CeCl₃ by cyanide groups in K₃Co(CN)₆. The electron spin resonance offers a convincing proof that numerous oxygen vacancies were found in Co-CeO₂/C aerogels after the introduction of CeO₂. The developed Co-CeO₂/C aerogels showed an outstanding electrochemical performance for both OER and ORR in comparsion with RuO₂ and Pt/C catalysts in 0.1 M KOH solution. A small overpotential (380 mV) and a low Tafel slope (99 mV dec^-1) were observed for OER, while the half-wave potential (0.75 V) and the onset potential (0.92 V) were high for ORR. The superior performance could be put down to the multihole heterostructure, multiple components and abundant oxygen vacancies. It was very helpful for the adsorption and the catalyzation of the reactants and the efficient mass transport of reagent/product. This work paves a neoteric method to synthesize a bifunctional hybrid catalyst with a highly efficient performance of energy conversion and storage.