Graphene Supported Silver Nanocrystals Preparation for Efficient Oxygen Reduction in Alkaline Fuel Cells

Abstract

The silver nanocrystals (AgNCs) anchored on graphene oxide (GO) catalysts have been synthesized by a facile chemical reduction and nontemplate method using ascorbic acid (AA) as reducing agent and have successfully employed as a cathode catalyst for oxygen reduction reaction (ORR) in direct alkaline fuel cells (DAFCs). The morphological characterizations demonstrate that the AgNCs have crystalline form and grafted onto reduced graphene oxide (AgNCs/rGO_AA). Comparatively better dispersion and higher population of AgNCs have observed on AA treated AgNCs/rGO than NaBH 4 which is known as conventional reducing agent. The electrochemical catalysis in 0.1 M KOH electrolyte has demonstrated that the AgNCs/rGO_AA has an excellent electrocatalytic activity for ORR in alkaline media compared to the other tested electrodes. Particularly, it shows 40% higher mass activity with large specific activity against 20 wt% Pt/C with faster electron transfer rate per O 2 . Moreover, the reaction kinetic parameters have confirmed that the ORR at AgNCs/rGO_AA catalyst not only follows a 4e -process with lowering H 2 O 2 formation but also proceeds on with good stability and fuel selectivity in DAFCs. The oxygen reduction reaction (ORR) is an interesting research area and already attracted widespread attention of researches from all over the world because of its important role in the application of energy storage and conversion devices, such as fuel cells (FCs) and metal−air batteries in alkaline media.1-4 Due to superior energy conversion efficiency and potential for providing clean energy, FCs are in the main attention as next generation energy sources. 5,6 As the FCs consists of anode and cathode electrodes, the greatest effect on the performance of FCs is the oxidation/reduction reaction kinetics occurring at the respective electrodes. Unfortunately, the sluggish kinetic rate of ORR at the cathode is the main obligation to be applied in industry. 6 Typically, the platinum (Pt) and/or Pt-based materials are known as the most efficient electrocatalyst in the cathode for ORR catalysis [7][8][9][10] but unfortunately, the Pt-based materials have faced many troubles such as its susceptibility to time dependent drift and CO poisoning, 11,12 slow electron-transfer kinetics, 13 high costs, limited supply, 14 and poor durability. 15 For those reasons, Pt has hindered the widespread commercialization of FCs technology. To overcome the cost challenges, significant efforts have focused on the development of alternative non-Pt catalysts that are based on mainly non-precious metals and/or various heteroatom-doped carbonaceous materials. [16][17][18] Among the non-Pt metal catalysts studied, silver (Ag)-based carbon nanomaterials have been explored as promising candidates with higher activity and stability in alkaline medium recently. [19][20][21][22] According to previous reports, the Ag is an ideal alternative of Pt because it is not only abundantly available in nature and much cheaper but also higher electrical and thermal conductive than Pt....

Oxygen Reduction Reaction on Silver Catalysts in Alkaline Media: a Minireview

“…[50] Graphene supported Ag nanoparticles prepared by reduction with ascorbic acid had better dispersion than those prepared using NaBH 4 , also the ORR specific and mass-activities were better for the former catalyst. [51] High electrocatalytic activity has also been demonstrated with silver on reduced graphene oxide prepared by simultaneous reduction of Ag + and graphene oxide. [52] Ag nanoparticles supported on graphene oxide/carbon spheres have been studied and found to have good ORR activity.…”

Improvement of Catalytic Activity of Platinum Nanoparticles Decorated Carbon Graphene Composite on Oxygen Electroreduction for Fuel Cells

“…The PtO reduction peak located around 0.7 V and the H 2 adsorption/desorption peaks at the range of 0.4 to 0 V in the backward CV scan was clearly appeared in all curves. The electrochemical surface area (ECSA) of all Pt-containing catalysts was derived from the Coulombic charge (Q) that are associated with H 2 adsorption-desorption on Pt-site using Equation (1) [55,56]. The ECSA of Pt-containing catalysts was calculated as 63, 77 and 65 m 2 g −1 Pt , while the Pt-loading was 28.3, 23.3 and 20.8 µg Pt cm −2 for the Pt/C, Pt/C 8 :G 2 and Pt/C 6 :G 4 , respectively.…”

“…where Q o is the charge associated with the H 2 adsorption/desorption region, Q r is the charge required for the monolayer adsorption of H 2 on Pt surface (assumed to be 210 µC cm −2 ) [55,56] and m is the Pt-mass loading (in µg cm −2 ).…”

3D graphene preparation via covalent amide functionalization for efficient metal-free electrocatalysis in oxygen reduction

“…Huge effort has been expended in the search for sustainable and renewable sources of green and clean energy because of the increasing demand and environmental impact of traditional energy resources, such as, fossil fuels 18 19 . In this regard, FCs have received significant attention as next-generation energy sources 20 21 because they directly generate electricity by electrochemically reducing oxygen and by oxidizing fuel into water as only the by-product.…”

“…In this regard, FCs have received significant attention as next-generation energy sources 20 21 because they directly generate electricity by electrochemically reducing oxygen and by oxidizing fuel into water as only the by-product. Direct ORR 8 21 22 catalysis involving four electrons is an interesting research area because of its important role in the application of energy conversion devices, such as FCs and metal-air batteries in alkaline media 18 19 20 21 23 . Novel metals, such as platinum (Pt) and its alloy materials are regarded as the most efficient electrocatalysts for ORR in cathodes 24 25 .…”