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Nitrogen-Doped Carbon Stabilized Ru Nanoclusters as Excellent Catalyst for Hydrogen Production Hua Wang, Caili Xu, Qian Chen, Mei Ming, Yi Wang, Ting Sun, Yun Zhang, Daojiang Gao, Jian Bi, and Guangyin Fan ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04823 • Publication Date (Web): 28 Nov 2018 Downloaded from http://pubs.acs.org on December 4, 2018
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Nitrogen-Doped Carbon Stabilized Ru Nanoclusters as Excellent Catalyst for Hydrogen Production Hua Wang, Caili Xu, Qian Chen, Mei Ming, Yi Wang, Ting Sun, Yun Zhang*, Daojiang Gao, Jian Bi and Guangyin Fan*
College of Chemistry and Materials Science, Sichuan Normal University, 5 Jingan Road, Chengdu 610068, China * Corresponding author Email:
[email protected] (Y. Zhang) Email:
[email protected] (G.Y. Fan)
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Abstract
The synthesis of ruthenium nanoclusters (NCs) is crucially important but challenging for hydrogen production. By taking advantage of confinement effect of nanopores in 3D porous carbon and urea as nitrogen source, we develop a straightforward method for preparation of uniform Ru NCs and simultaneous nitriding of the carbon scaffolds (Ru/3DNPC). The resulting Ru/3DNPC-500 had a measured overpotential of 15 mV at 10 mA cm-2 toward HER as well as very high turnover frequency (molH2 (mol Ru min)1)
for hydrolytic decomposition of ammonia–borane, outperforming many previously
reported Ru-based catalysts. Ru NCs confined in 3DNPC substrate can supply numerous catalytically active sites for the reactions, thereby leading to high catalytic activity. The present synthetic strategy could open a new direction for preparing metal NCs catalysts. Keywords: Electrolytic water splitting; Ammonia–borane hydrolytic decomposition; Ruthenium nanoclusters; Nitrogen-doping; Hydrogen evolution
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Introduction Hydrogen evolution from water electrolysis is considered as a convenient and effective strategy to apply hydrogen energy.1 Electrochemical water splitting to produce hydrogen is hindered by the serious electrode polarizations.2-3 Previous studies have shown that supported Pt catalysts display excellent catalytic performance toward HER, whereas their high-cost and limited reserves greatly restrict the practical applications.4 As one of Pt-group noble metals, ruthenium (Ru) is more favorable because of its featured advantages of low-cost and similar hydrogen bond strength compared to Pt.5 Thus, Ru is regarded as an ideal HER electrocatalyst and a couple of works about Rubased electrocatalysts have been developed.6-10 Especially, Ru deposited on nitrogen (N)-doped carbon materials, which was synthesized through the pyrolysis of the mixture of Ru precursor and N resource, have shown advanced electrocatalytic activity for HER.2, 11-12 Nevertheless, the facile preparation of Ru particle with ultrafine size (sub-2 nm) and homogeneous dispersity by using such high-temperature pyrolysis approach is highly desirable but still very challenging. Except for water electrolysis, hydrolytic decomposition of ammonia–borane (AB) has been regarded as an alternative method for hydrogen evolution.13-15 Among the catalysts that have been developed, Rubased materials are attractive for hydrolytic decomposition of AB.16-19 However, the catalytic activities of developed Ru catalysts are not satisfied enough compared with Pt-based catalysts.4,
20
Developing efficient Ru-based catalytic materials with high
performance for HER and hydrolytic decomposition of AB remains challenging.
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In most cases, the catalytic performances of supported metal catalysts are sizedependent and usually their reactivities are promoted with decreasing size of active components. Thus, supported metal nanoparticles (NPs) with small sizes have captured substantial attention because of their featured advantages of high surface-to-volume ratios and predominantly exposed surface-active atoms in comparison with their bulk counterparts.21 Considering the advanced size effect of metal NPs on the catalytic property, it can be expected that transformation of NPs to nanoclusters (NCs) is an ideal strategy to boost the reactivity because of the increased undercoordinated atoms of the metal NCs.21 However, the metal NCs are unstable and lead to the formation of particles in large sizes because of their high surface energies.22-23 Commonly, ultrafine metal NCs are always synthesized with surfactants to prohibit their overgrowth during the syntheses. Nevertheless, the existence of surfactants leads to the coverage of the active sites of metal NCs and reduces the catalytic activity. The present strategies for removal of the surfactants always lead to the decreased catalytic performance. Recently, Ndoped carbon is proven to be an efficient substrate to synthesize noble metal catalysts without any surfactants. Various kinds of N resources are used for preparing N-doped carbon supported Ru-based catalysts. For instance, single-atomic Ru dispersed on Ngraphene and N-doped carbon nanofibers were prepared in NH3 atmosphere.
24-25
In
addition, Ru NPs deposited C2N layers were synthesized through pyrolysis of the polycondensation
product
of
hexaketocyclohexane
and
hexaaminobenzene
trihydrochloride with RuCl3.12 Although satisfactory results have been achieved, the present methods of N-doping still suffer from poisonous atmosphere or using rare and
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expensive N-rich materials as N sources. Thus, Synthesis of ultrasmall Ru NPs (
