Fundamental Study of Facile and Stable Hydrogen Evolution Reaction at Electrospun Ir and Ru Mixed Oxide Nanofibers

Abstract

Electrochemical hydrogen evolution reaction (HER) has been an interesting research topic in terms of the increasing need of renewable and alternative energy conversion devices. In this article, IrRuO (y = 0 or 2) nanofibers with diverse compositions of Ir/IrO and RuO are synthesized by electrospinning and calcination procedures. Their HER activities are measured in 1.0 M NaOH. Interestingly, the HER activities of IrRuO nanofibers improve gradually during repetitive cathodic potential scans for HER, and then eventually reach the steady-state consistencies. This cathodic activation is attributed to the transformation of the nanofiber surface oxides to the metallic alloy. Among a series of IrRuO nanofibers, the cathodically activated IrRuO shows the best HER activity and stability even compared with IrO and RuO, commercial Pt and commercial Ir (20 wt % each metal loading on Vulcan carbon), where a superior stability is possibly ascribed to the instant generation of active Ir and Ru metals on the catalyst surface upon HER. Density functional theory calculation results for hydrogen adsorption show that the energy and adsorbate-catalyst distance at metallic IrRu are close to those at Pt. This suggests that mixed metallic Ir and Ru are significant contributors to the improved HER activity of IrRuO after the cathodic activation. The present findings clearly demonstrate that the mixed oxide of Ir and Ru is a very effective electrocatalytic system for HER.

Metal Nanotube/Nanowire-Based Unsupported Network Electrocatalysts

“…In this regard, although very promising results have been obtained in the individual half-cell reactions, it continues to be difficult to implement nano-network catalysts in membrane electrode The strategies employed for improving the activity, selectivity, and metal utilization of electrospun metal catalysts relate to those outlined in the previous paragraphs. They include the creation of additional surface area (e.g., by moving from the solid nanowire to the hollow nanotube morphology [131], the introduction of pores ( Figure 11B-G) [136,138,139]), improving the metal utilization by reducing the nanotube wall thickness [131] or the nanowire diameter (while avoiding bead formation [140]), and the exploitation of catalytic synergies of bimetallic or mixed oxide-metal systems [129,131,132]. Regarding the inclusion of metal oxides, it is important to highlight the potential value of inverse supporting for metal nano-network catalysts (i.e., the deposition of traces of a support material such as metal oxides onto an underlying metal substrate [141]).…”

“…After electrospinning, the polymer is removed by pyrolysis, which results in the formation of either oxidic (e.g., CuO [126], Fe 2 O 3 [128], CoO [128] or NiO [128]) or metallic (e.g., Pt [127]) nanowires of varying purity [127], depending on the reaction conditions and the nobility of the metal. The oxidic fibers are typically transformed into metal by reduction in H 2 atmosphere at elevated temperatures [126,128], but in situ reduction during application in the hydrogen evolution reaction also has been reported [129]. Also, it is possible to electrospin concentrated nanoparticle suspensions, followed by sintering, as was demonstrated for Au nanowires [130].…”

“…Like the closely related 3D nanotube and nanowire network catalysts, the electrospun variants are typically applied in electrochemical (bio)sensing [133], electrochemical energy conversion reactions (e.g., methanol electrooxidation [127] and oxygen reduction [131,132,136]), or water electrolysis [129], and often exhibit excellent durability [131,136]. Implementing electrospun fiber mats composed of conventional carbon-supported Pt, ionomer, and polymer binder as fuel cell electrodes showed increased performance compared to conventional spray-coated catalyst layers, which was explained by the open-porous network architecture, its high density of accessible active sites, and its improved water management [137].…”

Recent Advances in 1D Electrospun Nanocatalysts for Electrochemical Water Splitting

“…Noble metal Pt is well‐known as the best HER catalytic material as it shows high current density, low overpotential, and low Tafel slope (30 mV dec −1 ) in acidic condition. [ 91–94 ] However, Pt is easily poisoned by UPD due to the existence of trace metal ions in the electrolytes. [ 95 ] Fortunately, nanomaterials after the oxidative treatment have been reported to exhibit high catalytic activity for a long time without UPD problem.…”

Recent Progress of Ruthenium‐based Nanomaterials for Electrochemical Hydrogen Evolution

“…[37] Moreover, unlike metallic Ru and the state-of-art Pt, Ru oxides were not susceptible to be poisoned by the less active metals in the electrolyte through underpotential deposition (known as Pt contamination). [38] In this regard, oxidative treatment of Ru could be an effective strategy for catalysts preparation. [39] However, the relatively poor electrical conductivity and large size of Ru-oxides were main factors that seriously limited their catalytic activity.…”