FeCoNiMnCr High-Entropy Alloy Nanoparticle-Grafted NCNTs with Promising Performance in the Ohmic Polarization Region of Fuel Cells

Tailored Design of Mesoporous Nanospheres with High Entropic Alloy Sites for Efficient Redox Electrocatalysis

High Entropy Alloys (HEAs) are a versatile material with unique properties, tailored for various applications. They enable pH-sensitive electrocatalytic transformations like hydrogen evolution reaction (HER) and hydrogen oxidation reactions (HOR) in alkaline media. Mesoporous nanostructures with high surface area are preferred for these electrochemical reactions, but designing mesoporous HEA sis challenging. To overcome this challenge, a low-temperature triblock copolymer-assisted wet-chemical approach is developed to produce mesoporous HEA nanospheres composed of PtPdRuMoNi systems with sufficient entropic mixing. Owing to active sites with inherent entropic effect, mesoporous features, and increased accessibility, optimized HEA nanospheres promote strong HER/HOR performance in alkaline medium. At 30 mV nominal overpotential, it exhibits a mass activity of ≈167 (HER) and 151 A gPt -1 (HOR), far exceeding commercial Pt-C electrocatalysts (34 and 48 A gPt -1) and many recently reported various alloys. The Mott-Schottky analysis reveals HEA nanospheres inherit high charge carrier density, positive flat band potential, and smaller charge transfer barrier, resulting in better activity and faster kinetics. This micelle-assisted synthetic enable the exploration of the compositional and configurational spaces of HEAs at relatively low temperature, while simultaneously facilitating the introduction of mesoporous nanostructures for a wide range of catalytic applications.

Noble metal-free FeCoNiMnV high entropy alloy anchored on N-doped carbon nanotubes with prominent activity and durability for oxygen reduction and zinc-air batteries

Efficient and stable oxygen reduction reaction (ORR) catalysts are essential for constructing reliable energy conversion and storage devices. Herein, we prepared noble metal-free FeCoNiMnV high-entropy alloy supported on nitrogen-doped carbon nanotubes (FeCoNiMnV HEA/N-CNTs) by a one-step pyrolysis at 800 °C, as certificated by a set of characterizations. The graphitization degree of the N-CHTs was optimized by tuning the pyrolysis temperature in the control groups. The resultant catalyst greatly enhanced the ORR characteristics in the alkaline media, showing the positive onset potential (Eonset) of 0.99 V and half-wave potential (E1/2) of 0.85 V. More importantly, the above FeCoNiMnV HEA/N-CNTs assembled Zn-air battery exhibited a greater open-circuit voltage (1.482 V), larger power density (185.12 mW cm-2), and outstanding cycle stability (1698 cycles, 566 h). This study provides some valuable insights on developing sustainable ORR catalysts in Zn-air batteries.

Spatial Confinement of Pt Nanoparticles in Carbon Nanotubes for Efficient and Selective H2 Evolution from Methanol

H2 generation from methanol-water mixtures often requires high pressure and high temperature (200-300 °C). However, CO can be easily generated and poison the catalytic system under such high temperature. Therefore, it is highly desirable to develop the efficient catalytic systems for H2 production from methanol at room temperature, even at sub-zero temperatures. Herein, carbon nanotube-supported Pt nanocomposites are designed and synthesized as high-performance nano-catalysts, via stabilization of Pt nanoparticles onto carbon nanotube (CNT), for H2 production upon methanol dehydrogenation at sub-zero temperatures. Therein, the optimal Pt/CNT nanocomposite presents the superior catalytic performance in H2 production upon methanol dehydrogenation at the expense of B2(OH)4, with the TOF of 299.51 min-130 oC. Compared with other common carriers, Pt/CNT exhibited the highest catalytic performance in H2 production, emphasizing the critical role of CNT in methanol dehydrogenation. The confinement of Pt nanoparticles by CNTs is conducive to inhibiting the aggregation of Pt nanoparticles, thereby significantly increasing its catalytic performance and stability. The kinetic study, detailed mechanistic insights, and density functional theory (DFT) calculation confirm that the breaking of O─H bond of CH3OH is the rate-controlling step for methanol dehydrogenation, and both H atoms of H2 are supplied by methanol. Interestingly, H2 is also successfully produced from methanol dehydrogenation at -10 °C, which absolutely solves the freezing problem in the H2 evolution upon water-splitting reaction.

High entropy alloying strategy for accomplishing quintuple-nanoparticles grafted carbon towards exceptional high-performance overall seawater splitting

High entropy alloys (HEAs), a novel class of material, have been explored in terms of their excellent mechanical properties. Seawater electrolysis is a step towards sustainable production of carbon-neutral fuels such as H2, O2, and industrially demanding Cl2. Herein, we report a practically viable FeCoNiMnCr HEA nanoparticles system grafted on a conductive carbon matrix for promising seawater electrolysis. The comprehensive kinetics analysis of the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and chlorine evolution reaction (CER) confirms the effectiveness of our system. As an electrocatalyst, HEAs grafted on carbon black show trifunctionality with promising kinetics, selectivity and enduring performance, towards seawater splitting. We optimize high entropy alloy decorated/grafted carbon black (HEACB) catalysts, studying their synthesis temperature to scrutinize the effect of alloy formation variation on the catalysis efficacy. During the catalysis, selectivity between two mutually competing reactions, CER and OER, in the electrochemical catalysis of seawater is controlled by the reaction media pH. We employ Mott-Schottky measurements to probe the band structure of the intrinsically induced metal-semiconductor junction in the HEACB catalyst, where the carrier density and flat band potential are optimized. The HEACB sample provides promising results towards overall seawater electrolysis with a net half-cell potential of about 1.65 V with good stability, which strongly implies its broad practical applicability.

Synthesis of a carbon-wrapped microsphere MoO2/Mo2C heterojunction as an efficient electrocatalyst for the oxygen reduction reaction and the hydrogen evolution reaction

The development of non-noble metal catalysts for the optimization of conversion and storage devices is an important research topic. Hence, the microsphere MoO2/Mo2C/C heterojunction composites, which play an important role in the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER), were synthesized using the solvothermal-sintering method. The results revealed that the as-prepared composite exhibited better ORR and HER catalytic performances than those of MoO2/Mo2C and Vulcan XC-72R (carbon black), and approaching that of commercial Pt/C. At the same time, it has a superior methanol tolerance and electrochemical stability than that of the commercial Pt/C. The excellent performance may be attributed to the synergistic effect of the MoO2/Mo2C heterostructure, highly conductive Vulcan XC-72R, and oxygen vacancies (Ov). This research offers new insights into the design and synthesis of cost-effective, environmentally friendly heterojunction composite catalysts used as a high-performance cathode material in fuel cells and water splitting.

FeNiCrCoMn High-Entropy Alloy Nanoparticles Loaded on Carbon Nanotubes as Bifunctional Oxygen Catalysts for Rechargeable Zinc-Air Batteries

An efficient and stable bifunctional oxygen catalyst is necessary to complete the application of the rechargeable zinc-air battery. Herein, an economical and convenient process was adopted to successfully coat high-entropy alloy Fe₁₂Ni₂₃Cr₁₀Co_55-xMn_x nanoparticles on carbon nanotubes (CNTs). In 0.1 M KOH solution, with a bifunctional oxygen overpotential (ΔE) of only 0.7 V, the catalyst Fe₁₂Ni₂₃Cr₁₀Co₃₀Mn₂₅/CNT exhibits excellent bifunctional oxygen catalytic performance, exceeding most catalysts reported so far. In addition, the air electrode assembled with this catalyst exhibits high specific capacity (760 mA h g^-1) and energy density (865.5 W h kg^-1) in a liquid zinc-air battery, with a long-term cycle stability over 256 h. The density functional theory calculation points out that changing the atomic ratio of Co/Mn can change the adsorption energy of the oxygen intermediate (*OOH), which allows the ORR catalytic process to be accelerated in the alkaline environment, thereby increasing the ORR catalytic activity. This article has important implications for the progress of commercially available bifunctional oxygen catalysts and their applications in zinc-air batteries.

PtFeCoNiCu high-entropy solid solution alloy as highly efficient electrocatalyst for the oxygen reduction reaction

Searching for an efficient, durable, and low cost catalyst toward oxygen reduction reaction (ORR) is of paramount importance for the application of fuel cell technology. Herein, PtFeCoNiCu high-entropy alloy nanoparticles (PFCNC-HEA) is reported as electrocatalyst toward ORR. It shows remarkable ORR catalytic mass activity of 1.738 A mg^-1 _Pt at 0.90 V, which is 15.8 times higher than that of the state-of-art commercial Pt/C catalyst. It also exhibits outstanding stability with negligible voltage decay (3 mV) after 10k cycles accelerated durability test. High ORR activity is ascribed to the ligand effect caused by polymetallic elements, the optimization of the surface electronic structure, and the formation of multiple active sites on the surface. In the proton exchange membrane fuel cell setup, this cell delivers a power density of up to 1.380 W cm^-2 with a cathodic Pt loading of 0.03 mg_Pt cm^-2, demonstrating a promising catalyst design direction for highly efficient ORR.