Ru-tweaking of non-precious materials: The tale of a strategy that ensures both cost and energy efficiency in electrocatalytic water splitting
23 Mar 2021-Journal of Materials Chemistry (Royal Society of Chemistry (RSC))-Vol. 9, Iss: 11, pp 6710-6731
TL;DR: In this article, a detailed review of water splitting electrocatalysis and mechanisms involving Ru is given with insights on the phenomena that make it an active interface for water electrolysis, and the same is also benchmarked against their performance at different conditions.
Abstract: Most better performing water splitting electrocatalysts are scarce, and their use increases the cost of production of H2via electrolysis. Among the best performing noble/precious metal electrocatalysts, Ru is most notable because it acts as an excellent electrocatalyst for both oxidation and reduction reactions of water responsible for the H2 production. In fact, Ru outperforms Pt/C as the state-of-the-art water reduction electrocatalyst in alkali. However, the cost-wise more expensive Ru (than Pt and Ir) could not be extensively used in water electrolysis to avoid further increase in the cost of H2 production. Recently, there has been a renewed interest in Ru and is being intensively investigated with various structural and chemical modifications at the nano-level for catalytic water electrolysis with and without other materials. However, there is no comprehensive review that summarizes and analyzes recent developments in water splitting electrocatalysts that are modulated with Ru. Hence, this review is devoted to bringing out the strategies involved in harvesting the best of water splitting electrocatalysts by Ru-tweaking. The same is also benchmarked against their performance at different conditions. Besides, a detailed note on water splitting electrocatalysis and mechanisms involving Ru are given with insights on the phenomena that make it an active interface for water electrolysis.
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TL;DR: In this paper, hollow nanostructured Ni5P2/FeP4 nanoboxes (NiFeP NBs) are designed and synthesized as pre-catalysts.
Abstract: Transition metal phosphides (TMPs) have been reported as efficient pre-catalysts for the oxygen evolution reaction (OER) in alkaline media. In situ generated metal oxyhydroxides on the surface of TMPs serve as real active sites. However, the reconstruction of most of the reported TMPs is incomplete and the active components cannot be fully used. Herein, hollow nanostructured Ni5P2/FeP4 nanoboxes (NiFeP NBs) are designed and synthesized as pre-catalysts. During the OER, the NiFeP NBs deeply reconstruct into low-crystalline and ultrathin NiOOH/FeOOH nanosheet assembled nanoboxes (NiOOH/FeOOH NBs). In situ Raman spectroscopy and ex situ characterization studies provide evidence that the hollow nanostructure facilitates the deep reconstruction of NiFeP NBs. Benefiting from the hierarchical hollow structure, the abundant interface between NiOOH and FeOOH, and plentiful defects, the reconstructed NiOOH/FeOOH NBs exhibit superior OER activity and excellent stability. Density functional theory (DFT) calculations reveal that the Fe–Ni dual sites in the NiOOH/FeOOH interface may be the possible active sites.
123 citations
TL;DR: In this article, the authors proposed to normalize turnover frequency (TOF) by Faradaic efficiency (FE) to determine the number of active sites and real surface area for all kinds of materials.
Abstract: For decades, turnover frequency (TOF) has served as an accurate descriptor of the intrinsic activity of a catalyst, including those in electrocatalytic reactions involving both fuel generation and fuel consumption. Unfortunately, in most of the recent reports in this area, TOF is often not properly reported or not reported at all, in contrast to the overpotentials at a benchmarking current density. The current density is significant in determining the apparent activity, but it is affected by catalyst-centric parasitic reactions, electrolyte-centric competing reactions, and capacitance. Luckily, a properly calculated TOF can precisely give the intrinsic activity free from these phenomena in electrocatalysis. In this Viewpoint we ask: 1) What makes the commonly used activity markers unsuitable for intrinsic activity determination? 2) How can TOF reflect the intrinsic activity? 3) Why is TOF still underused in electrocatalysis? 4) What methods are used in TOF determination? and 5) What is essential in the more accurate calculation of TOF? Finally, the significance of normalizing TOF by Faradaic efficiency (FE) is stressed and we give our views on the development of universal analytical tools to determine the exact number of active sites and real surface area for all kinds of materials.
115 citations
TL;DR: In this paper, a review of the research progress on hydrogen evolution reaction (HER) electrocatalysts and the relevant describing parameters for HER performance are briefly introduced, including electronic effect modulation, support engineering, structure design, and maximum utilization (single atom) are discussed.
Abstract: The investigation of highly effective, durable, and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) is a prerequisite for the upcoming hydrogen energy society. To establish a new hydrogen energy system and gradually replace the traditional fossil-based energy, electrochemical water-splitting is considered the most promising, environmentally friendly, and efficient way to produce pure hydrogen. Compared with the commonly used platinum (Pt)-based catalysts, ruthenium (Ru) is expected to be a good alternative because of its similar hydrogen bonding energy, lower water decomposition barrier, and considerably lower price. Analyzing and revealing the HER mechanisms, as well as identifying a rational design of Ru-based HER catalysts with desirable activity and stability is indispensable. In this review, the research progress on HER electrocatalysts and the relevant describing parameters for HER performance are briefly introduced. Moreover, four major strategies to improve the performance of Ru-based electrocatalysts, including electronic effect modulation, support engineering, structure design, and maximum utilization (single atom) are discussed. Finally, the challenges, solutions and prospects are highlighted to prompt the practical applications of Ru-based electrocatalysts for HER.
82 citations
TL;DR: In this article, the authors developed ultrafine Ir nanoparticles coupled with FeP/FeOOH with abundant interfaces on iron foam (FF) via facile corrosive strategies, which not only exposes abundant active centers, but also enhances the electron transport efficiently.
Abstract: In order to generate clean hydrogen fuel, it is necessary to exploit bifunctional catalysts with high activity and excellent stability for overall water-splitting. Herein, we develop ultrafine Ir nanoparticles coupled with FeP/FeOOH with abundant interfaces on iron foam (FF) via facile corrosive strategies. The ingeniously designed catalyst structure not only exposes abundant active centers, but also enhances the electron transport efficiently. Thus, the FF–NaCl–Ir–P catalyst exhibits outstanding catalytic activities for the OER (169 mV at 10 mA cm−2) and HER (69 mV at 10 mA cm−2) in 1 M KOH, which was better than most of the previously reported catalysts. For water-splitting, it only needs 1.47 V to reach 10 mA cm−2, and its performance hardly deteriorates after 50 hours test at a large-current density of 1000 mA cm−2. The overall water-splitting can also be motivated by simple sustainable energy, such as solar, wind and thermal energies.
29 citations
TL;DR: In this article, a strong disagreement between non-Faradaic Cdl and Faradaic oxygen evolution reaction (OER) activity trend between stainless steel and bleached stainless steel (BSS) was shown.
26 citations
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