Noble-metal-based high-entropy-alloy nanoparticles for electrocatalysis

Since the two seminal papers were published independently in 2004, high-entropy-alloys(HEAs) have been applied to structural and functional materials due to the enhanced mechanical properties, thermal stability, and electrical conductivity. In recent years, HEA nanoparticles(HEA-NPs) were paid much attention to in the field of catalysis for the promoted catalytic activity. Furthermore, the various ratios among the metal components and tunable bulk and surface structures enable HEAs have big room to enhance the catalytic performance. Especially, noble-metal-based HEAs displayed significantly improved performance in electrocatalysis, where the ‘core effects’ were employed to explain the superior catalytic activity. However, it is insufficient to understand the essential mechanism or further guide the design of electrocatalysts. Structure–property relationship should be disclosed for the catalysis on HEA-NPs to accelerate the process of seeking high effective and efficient electrocatalysts. Therefore, we summarized the recent advances of noble-metal-based HEA-NPs applied to electrocatalysis, such as hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, methanol oxidation reaction, ethanol oxidation reaction, formic acid oxidation reaction, hydrogen oxidation reaction, carbon dioxide reduction reaction and nitrogen reduction reaction. For each electrocatalytic reaction, the reaction mechanism and catalyst structure were presented, and then the structure–property relationship was elaborated. The review begins with the development, concept, four ‘core effect’ and synthesis methods of HEAs. Next,the electrocatalytic reactions on noble-metal-based HEA-NPs are summarized and discussed independently. Lastly, the main views and difficulties pertaining to structure–property relationship for HEAs are discussed.

Nanostructured amorphous Fe_(29)Co_(27)Ni_(23)Si_(9)B_(12) high-entropy-alloy:an efficient electrocatalyst for oxygen evolution reaction

Proximal configu ration of dissimilar metal atoms in amorphous high-entropy-alloys(HEAs) always re sult in interatomic d-band ligand effect,dense defect distribution,coordinatively unsaturated sites,high potential energy,and loose atom bonding.Herein,nanostructured amorphous Fe_(29)Co_(27)Ni_(23)Si_(9)B_(12) HEA ribbon is fabricated via a melt spinning method combined with electrochemical corrosion etching process,which is applied as the potential oxygen evolution reaction electrocatalyst.It is found that there are micro/nano pits on the surface of etched amorphous Fe_(29)Co_(27)Ni_(23)Si_(9)B_(12) ribbons.Various elements of HEAs bond with each other to form a highly disordered configu ration,which could result in an optimized bonding energy and enhanced intrinsic catalytic activity.The electrocatalysis activity measurements indicate that the amorphous HEA endows a much higher activity than the crystalline one,which is further improved by the electrochemical etching treatment.Especially,the HEA ribbon etched for 3 h requires a low overpotential of 230 mV to afford 10 mA cm^(-2) current density.In addition,density functional theory calculations demonstrate that the amorphous structure can weaken the interaction between the surface of Fe_(29)Co_(27)Ni_(23)Si_(9)B_(12) alloy and the intermediates,leading to an optimized adsorption Gibbs free energy.

Free-Standing Multiscale Porous High Entropy NiFeCoZn Alloy as the Highly Active Bifunctional Electrocatalyst for Alkaline Water Splitting

In the endeavor of searching for highly active and stable electrocatalysts toward overall water splitting,high-entropy-alloys have been the intense subjects owing to their advanced physicochemical property.The non-noble metal free-standing multiscale porous NiFeCoZn high-entropy-alloy is in situ constructed on the surface layer of NiZn intermetallic and Ni heterojunction over nickel foam(NiFeCoZn/NiZn-Ni/NF)by one scalable dealloying protocal to fulfill the outstanding bifunctional electrocatalytic performances toward overall water splitting.Because of the high-entropy effects and specific hierarchical porous architecture,the as-made NiFeCoZn/NiZn-Ni/NF displays high intrinsic catalytic activities and durability toward both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)in alkaline media.In particular,the in-situ construction of bimodal porous NiFeCoZn high-entropy-alloy results in the small overpotentials(η1000=254/409 mV for HER and OER),low Tafel slopes,and exceptional long-term catalytic durability for 400 h.Expressively,the electrolyzer constructed with NiFeCoZn/NiZn-Ni/NF as both cathode and anode exhibits a low cell voltage of 1.72 V to deliver the current density of 500 mA·cm^(–2) for overall water splitting.This work not only provides a facile and scalable protocol for the preparation of self-supporting high-entropy-alloy nanocatalysts but also enlightens the engineering of high performance bifunctional electrocatalysts toward water splitting.