Gold aerogel supported on graphitic carbon nitride: an efficient electrocatalyst for oxygen reduction reaction and hydrogen evolution reaction

Abstract

Fabrication of high surface area interconnected porous network of metallic nanomaterials is important for their applications in various fields such as catalysis, sensors, and electrochemistry. Here we report a facile bottom up synthesis of high surface area and porous, gold aerogel supported on carbon nitride sheets (CNx). The reduction of HAuCl4 in presence of carbon nitride nanosheets using sodium brohydride and ultrasonic treatment produces gold aerogel supported on carbon nitride (Au-aerogel-CNx). When the reduction of HAuCl4 in presence CNx nano sheets was done only with ultrasonication, highly dispersed ultra small ( ~2 nm) gold nanoparticles on CNx sheets (AuNPs-CNx) were formed. The Au aerogel supported on CNx sheets was well characterized by powder X-ray diffraction, tunneling electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, UV-Visible and Xray photo electron spectroscopic methods. The Au-aerogel-CNx and AuNPs-CNx composites exhibited superior electro catalytic activity towards oxygen reduction reaction (ORR) in alkaline and acidic media. The Au-aerogel-CNx composite show ORR onset potentials at 0.92 V and 0.43 V (Vs RHE) in 0.5 M KOH and H2SO4 solution. The four electron oxygen reduction proceess occurs at these supported catalysts in both alkaline and acidic media. In alkaline (KOH) medium the onset potential at Au-aerogel-CNx is more positive ( ~ 30 mV) than that of commercial Pt/C catalyst. The composites display excellent methanol tolerance and comparable durability with commercial Pt/C. Furthermore, the Au-aerogel-CNx composites exhibited high catalytic activity for hydrogen reduction reaction (HER) with small onset potential of -30 mV and a Tafel slope of 53 mV dec -1 in acidic medium. At a small Au loading of 0.130 mg cm -2 , this catlyst also exhibit a current density of 10 mA cm -2 at a low overpotential of -185 mV with an excellent stability. The ORR and HER performaneces on porous, Au-aerogel-CNx composites is better than that of AuNPs-CNx catalyst and commercial flat gold electrode. The superior ORR and HER activity at Au-aerogel-CNx composite are originated from the unique synergistic effects between porous Au network and carbon nitride (CNx) support. Please do not adjust margins Please do not adjust margins approaches are available in literature for synthesis of different non metal aerogel such as carbon aerogel 11 , silica aerogel 12 , organic-inorganic hybrid 13 , metal oxide 14 , and metal chalcogenides 15 . But only few methods are available for the production of metal aerogel 8,16,17,18 . For example, Eychmüller and coworkers 8,16 have reported synthesis for monometallic, bi-metallic and composite aerogels based on controlled aggregation of metal nanoparticles using controllable destabilization and spontaneous gelation methods. Leventis and his co-workers 17,18 developed methods for synthesis of different metallic (Fe, cu, Ni, Co) aerogels by nanosmelting (sol-gel method) of hybrid polymer-metal oxide composit...

Bioreduction of Precious Metals by Microorganism: Efficient Gold@N‐Doped Carbon Electrocatalysts for the Hydrogen Evolution Reaction

“…However, to the best of our knowledge, Au nanoparticles as HER electrocatalysts are rare. [10] More importantly, recovery and reuse of precious metals (such as Au and Ag) derived from waste electronic equipment (such as mobile phones) is of environmental significance, and holds great potential for industrial commercialization. [11] Das and Marsili et al successfully prepared Au nanoparticles by bioreductive synthesis in R. oryzae cells; the biosynthetic process was considered economically viable and environmentally friendly.…”

Gold Nanoparticle/Multi‐walled Carbon Nanotube Hybrid as a Stable Catalyst for the Oxygen Reduction Reaction

“…The TG analysis of the Au/MWNTs hybrid shown in Figure S1a in Supporting Information indicates that the sample is rather stable at the temperature lower than 400 °C, which decomposes at higher temperature with 28.6 % of the mass remained at 1000 °C. In contrast, there is no residual for the oxidized MWNTs at the temperature higher than 650 °C in Figure S1b in the Supporting Information, and hence the loading of Au NPs is estimated by the pyrolytic data as 28.6 %, which means about 98.6 % of HAuCl 4 has been reduced to Au NPs (with the calculation details in the Supporting Information), suggesting that the one‐pot synthesis leads to a high yielding of mono‐dispersed Au NPs in comparison to previous reports ,,,…”

“…As for the effect of supporting substrates, Kundu et al. investigated the hybrid of Au aerogel (less than 1 nm) on CN x nanosheets, which manifested even better catalytic activity than commercial Pt/C catalysts in alkaline solutions owing to the superior synergistic effect between Au NPs and CN x . Similarly, the Au/AlPO 4 nanocomposites also displayed high catalytic activity in both alkaline and acidic solutions, due to the electronic interactions between Au and AlPO 4 .…”

“…Up to now, thiol, oleylamine, L‐ascorbic acid, citrate, CTAB etc. have been utilized to protect the Au NPs,,,, which consequently blocked the mass transport and electron transfer to some extent on the surface of Au catalysts ,. Under this context, a few approaches have been developed to remove the capping molecules, such as thermal treatment, UV‐exposure and atomic hydrogen, which normally end up with the growth of Au nanocrystals .…”

Understanding the cooperative atomic motion and shape change of ultrasmall Au nanoparticles below the premelting temperature

“…[3][4][5] To trigger the high activity of gold, the NPs are oen sufficiently small, ranging from 1-5 nm, the size-and shape-dependent performances therefore become much more prominent. [6][7][8][9] In particular, Au NPs with a diameter of 1-2 nm have been reported with signicantly improved catalytically activity than the larger counterparts. [10][11][12] A classic example is the 55-atom gold cluster ($1.4 nm) which showed superior selective oxidation activity using molecular oxygen.…”