Hierarchical Architectures Based on Ru Nanoparticles/Oxygen‐Rich‐Carbon Nanotubes for Efficient Hydrogen Evolution

Abstract

Highly active and durable electrocatalysts are essential for producing hydrogen fuel through the hydrogen evolution reaction (HER). Here, a uniform deposition of Ru nanoparticles strongly interacting with oxygen-rich carbon nanotube architectures (Ru-OCNT) through ozonation and hydrothermal approaches has been designed. The hierarchical structure of Ru-OCNT is made by self-assembly of oxygen functionalities of OCNT. Ru nanoparticles interact strongly with OCNT at the Ru/OCNT interface to give excellent catalytic activity and stability of the Ru-OCNT, as further confirmed by density functional theory. Owing to the hierarchical structure and adjusted surface chemistry, Ru-OCNT has an overpotential of 34 mV at 10 mA cm À 2 with a Tafel slope of 27.8 mV dec À 1 in 1 M KOH, and an overpotential of 55 mV with Tafel slope of 33 mV dec À 1 in 0.5 M H 2 SO 4 . The smaller Tafel slope of Ru-OCNT than Ru-CNT and commercial Pt/C in both alkaline and acidic electrolytes indicates high catalytic activity and fast charge transfer kinetics. The asproposed chemistry provides the rational design of hierarchically structured CNT/nanoparticle electrocatalysts for HER to produce hydrogen fuel.

Understanding the Atomic and Defective Interface Effect on Ruthenium Clusters for the Hydrogen Evolution Reaction

“…12,13 It is necessary to moderately weaken the H adsorption intensity on Ru sites via introducing substrates to improve catalytic performance. 10 The d centers for CNT−Ru, CNT−Fe−Ru, CNT−V−Ru, and CNT−V−Fe−Ru after H-absorbed are −1.68 eV, −1.77 eV, −1.72 eV, and −1.84 eV, respectively, suggesting that a CNT−V−Fe substrate can decrease the H adsorption intensity of the Ru site to the greatest extent according to the d-band theory. 16,58−60 Thus, CNT−V−Fe− Ru will show efficient HER catalytic performance.…”

“…But, the Ru-d electron densities near the E f for the CNT–Ru, CNT–Fe–Ru, CNT–V–Ru, and CNT–V–Fe–Ru are significantly enhanced, which implies Ru sites as the potential active centers for the HER . However, overly strong H adsorption intensity on Ru sites will prohibit the desorption step, thus resulting in a decreased HER performance. , It is necessary to moderately weaken the H adsorption intensity on Ru sites via introducing substrates to improve catalytic performance . The d centers for CNT–Ru, CNT–Fe–Ru, CNT–V–Ru, and CNT–V–Fe–Ru after H-absorbed are −1.68 eV, −1.77 eV, −1.72 eV, and −1.84 eV, respectively, suggesting that a CNT–V–Fe substrate can decrease the H adsorption intensity of the Ru site to the greatest extent according to the d-band theory. ,− Thus, CNT–V–Fe–Ru will show efficient HER catalytic performance.…”

“…Pt-based catalysts have so far shown state-of-the-art HER performance, while the scarce reserves and expensive prices substantially limit their large-scale commercial applications. , The relatively cost-effective ruthenium (Ru)-based materials have been extensively studied as potential substitutes as a result of similar physical as well as chemical properties with Pt and highly regulable electronic structures. − However, Ru-based catalysts still face significant challenges in improving their intrinsic activity for the HER. In particular, the high cohesive energy of Ru would lead to irreversible agglomeration and structural collapse during catalysis. , In addition, overstrong H adsorption intensity on Ru sites also prohibits the desorption step, thus resulting in the decreased HER performance. , Nevertheless, a few studies have demonstrated that the electronic structures of metal active sites could be effectively regulated through the interfacial interaction with substrates. ,− Therefore, the manipulation of binding moieties of metal–substrate interfaces would fundamentally address the hurdles that have confronted Ru and other transition metal-based catalysts.…”

“…In particular, the high cohesive energy of Ru would lead to irreversible agglomeration and structural collapse during catalysis. 10,11 In addition, overstrong H adsorption intensity on Ru sites also prohibits the desorption step, thus resulting in the decreased HER performance. 12,13 Nevertheless, a few studies have demonstrated that the electronic structures of metal active sites could be effectively regulated through the interfacial interaction with substrates.…”

“…Especially, the introduction of porous structure and heteroatoms (N, P, O, etc.) into carbon-based substrates efficiently increases the number of vacancy defects for stable immobilization of active sites with high dispersion. ,,− However, there are considerable challenges in adequately adjusting electronic structures of metal–substrate interfaces at the atomic level via accessible regulation strategies. Notably, carbon-supported single-atomic catalysts have been paid great attention since the advent of remarkably improved atomic utilization with highly tailorable electronic structures in comparison to bulk and nanocatalysts. − In this regard, one would expect carbon-supported single-atom materials to serve as substrates for loading active metallic catalysts.…”