Facile and Scalable Ambient Pressure Chemical Vapor Deposition-Assisted Synthesis of Layered Silver Selenide (β-Ag2Se) on Ag Foil as a Possible Oxygen Reduction Catalyst in Alkaline Medium

Abstract

Abstract Body: To alleviate the adverse impacts of utilizing fossil fuel reserves on the environment (global warming, greenhouse emissions), extensive research is being devoted to the development of alternative/renewable energy systems, which include: photovoltaics, fuel cells, batteries, etc. Among them, fuel cells are an excellent solution for energy conversion, where proton exchange membrane (PEM) fuel cells have a wide variety of applications. Some of these applications are portable systems, automotive, etc., where an important reaction occurring at the cathode is the oxygen reduction reaction (ORR). At the current stage in fuel cell technology, platinum (Pt)-based materials are the most practical catalysts1, which, undoubtedly, are the prime choice as the cathode catalyst for the electro-reduction of oxygen, but Pt-based catalysts are expensive. To reduce such costs in commercially viable fuel cells, extensive research is focused on developing alternative catalysts. Silver-based catalysts show a comparatively high thermodynamic stability and excellent catalytic activity over a wide pH range. The TMCs (O, S, Se, and especially Se-based chalcogenides) have attracted significant attention since selenium-based cluster compounds work. Selenium-based metal-rich TMCs catalysts exhibit good electrocatalytic activity, which is mainly attributed to selenium because it improves the electronic structure of the metal by preventing the electrochemical oxidation of metals in most transition metal chalcogenides, as seen for the cases of cobalt selenide and ruthenium selenide. Here, we present a high yield, industrially scalable, and the first-time report on the synthesis of silver selenide from silver foil and selenium powder using a two furnace atmospheric pressure-chemical vapor deposition (AP-CVD) system. We grew low temperature, LT-β-Ag2Se on Ag foil in the AP-CVD system using thermal annealing and leading to a hollow fern-like morphology material and its first-ever reported application as an ORR cathode catalyst. The exfoliated β-Ag2Se is characterized using XRD, EDS, HRTEM, AFM, and HRSEM to determine its stoichiometry and its hollow layered fern-like morphology. Differential scanning calorimetry (DSC) further confirms that the final product is the low-temperature phase β-Ag2Se. Electrochemical oxygen reduction reaction (ORR) of exfoliated β-Ag2Se exhibits sharp oxygen reduction current with an onset potential of 0.88 V/RHE under alkaline conditions, indicating the oxygen reduction property of β-Ag2Se. The large value of limiting current (3 mA cm-2) as well as small Tafel slope (68.5 mV dec-1) corroborates β-Ag2Se as a superior layered transition metal chalcogenide cathode material suitable for such energy-related applications (typically fuel cells and/or metal-air batteries). References (1) Ostroverkh, A.; Johánek, V.; Dubau, M.; Kúš, P.; Khalakhan, I.; Šmíd, B.; Fiala, R.; Václavu, M.; Ostroverkh, Y.; Matolín, V. Optimization of Ionomer-Free Ultra-Low Loading Pt Catalyst for Anode/Cathode of PEMFC via Magnetron Sputtering. Int. J. Hydrogen Energy 2019, 44 (35), 19344–19356. https://doi.org/10.1016/j.ijhydene.2018.12.206.