Contents lists available at ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem Oxygen reduction reaction on electrochemically deposited silver nanoparticles from non-aqueous solution Jonas Mart Linge a , Heiki Erikson a, ⁎ , Jekaterina Kozlova b , Väino Sammelselg a,b , Kaido Tammeveski a a Institute of Chemistry, University of Tartu, Ravila 14a, 50411 Tartu, Estonia b Institute of Physics, University of Tartu, W. Ostwald Str. 1, 50411 Tartu, Estonia ARTICLE INFO Keywords: Electrodeposition Ag nanoparticles Silver catalyst Oxygen reduction Electrocatalysis ABSTRACT Silver was electrodeposited onto glassy carbon electrode from 0.1 mM AgClO 4 acetonitrile solution containing 0.1 M LiClO 4 . The electrochemical deposition was carried out at constant potential of -0.5 V vs. SCE. The surface morphology was studied by scanning electron microscopy and the average particle size was determined to be 45 nm to 90 nm when increasing the deposition time from 10 s to 300 s. The rotating disk electrode (RDE) method was employed for oxygen reduction studies in 0.1 M KOH solution. It was determined that the final product for the reaction is water and the rate-determining step is the slow transfer of the first electron to O 2 molecule. The specific activities (SA) and mass activities (MA) were calculated from the RDE results and the latter was independent of the deposition time. The method used to determine electroactive surface area of Ag influenced substantially the determination of SA values. 1. Introduction The oxygen reduction reaction (ORR) is the performance limiting reaction in low-temperature fuel cells and the best electrocatalysts for ORR are platinum-based materials [1]. Due to the high cost of Pt cheaper alternatives are sought for [2,3]. Silver is a promising catalyst material for ORR in alkaline media [3,4]. Chatenet et al. demonstrated that on Pt and Ag, both bulk polycrystalline and highly dispersed on carbon, catalyse the ORR to form water and the kinetics are in the first order towards oxygen concentration in solution [5]. The ORR activity on Ag is slightly lower than on Pt but the price of the metals makes Ag essentially more favourable [6]. Most often the discussion of the ORR performance on Ag-based catalysts is concentrated on the number of electrons transferred per O 2 molecule (n). Blizanac et al. studied the ORR on low-index Ag single- crystal surfaces [7]. It was determined that the ORR on Ag is a structure sensitive reaction and the kinetics of the ORR increases in the order of Ag(100) ≤ Ag(111) < Ag(110). They suggested that the structure sensitivity may arise from potential-dependent adsorption of spectator hydroxyl ions or due to variations in activation energies. It was sug- gested that serial 4-electron pathway occurs most likely on Ag(hkl) in KOH. However, Wang et al. suggested that the Ag nanodecahedra en- closed by (111) facet catalyse the ORR via one-step four-electron re- action pathway [8]. To elaborate the differences in the ORR activity they modelled the system and concluded that the weaker adsorption of OH on Ag(111) facet provides higher number of active sites and thus leading to higher ORR activity on nanodecahedra as compared to na- nocubes enclosed by Ag(100). When electrochemical deposition is carried out in the presence of poly(vinyl pyrrolidone) then it inhibits the crystalline growth in the [111] direction and thus yielding particles with essentially only (111) facets [9]. The ORR on those formed Ag nanosheet arrays proceeds to form water. Similar Ag nanoplatelets have been obtained when using sodium citrate as capping agent [10]. The Ag particle size may affect the value of n, as the ORR on 174 nm particles showed higher electron transfer number than 4.1 nm Ag par- ticles [11]. However this might be similar to the findings by Neumann et al. who reported that the yield of water decreases with increasing the interdistance of particles [12]. In addition, when investigating the ORR on carbon-supported Ag nanoparticles it was found that the peroxide yield in solution phase with 10 wt% Ag/C was up to 10%, while for Ag/ C catalyst with 20 wt% and higher Ag content the ring currents sug- gested negligible H 2 O 2 production [13]. Garcia et al. calculated that 2.7 electrons are transferred to O 2 molecule on 10 wt% Ag/C and thus they suggested that oxygen is also partially reduced on carbon support [14]. 20 wt% Ag/C has been suggested to be the best loading in terms of current density and mass activity [15]. In that study the tolerance of methanol was also evaluated and it was concluded that Ag/C is less affected to methanol than Pt/C catalyst. Graphene-supported silver https://doi.org/10.1016/j.jelechem.2018.01.009 Received 18 July 2017; Received in revised form 5 January 2018; Accepted 6 January 2018 ⁎ Corresponding author. E-mail address: heiki.erikson@ut.ee (H. Erikson). Journal of Electroanalytical Chemistry 810 (2018) 129–134 Available online 07 January 2018 1572-6657/ © 2018 Published by Elsevier B.V. T