Ultra-Low Noble Metal Containing One-Dimensional Nanorods: High Performance Oer Electrocatalyst for Acid Mediated PEM Based Water Electrolysis

Abstract

The rising concerns of rapidly depleting conventional fossil fuels combined with the alarming global warming signs have made it imperative to explore the development of alternative clean, environmentally friendly and sustainable energy sources for alleviating our perpetual reliance on the high carbon foot print of fossil fuels. In order to achieve this goal, hydrogen (H2), a non-carbonaceous high efficiency fuel having higher energy density than petroleum based energy sources has garnered much attention over the years.1-2 Generation of clean and sustainable hydrogen via proton exchange membrane (PEM) based acid mediated water electrolysis is one of the most advantageous, efficient and reliable hydrogen production technologies.3-4 Though promising, commercial implementation of this technology is hindered by the need for expensive and environmentally scarce electrocatalysts belonging to the platinum group metals (PGM) such as Pt, RuO2, IrO2. PGM based electro-catalysts albeit known for their excellent electrochemical response for oxygen evolution reaction (OER), are also characterized by sluggish reaction kinetics.1, 5 Therefore, there is a need to identify, synthesize and develop novel reduced noble metal containing electro-catalysts displaying excellent electro-catalytic activity and robust long term electrochemical stability similar/superior to IrO2-the state of the art OER electrocatalyst in highly acidic operating conditions of OER. In addition, generating one-dimensional (1D) morphologies such as nanowires (NWs), nanorods (NRs) and nanotubes (NTs) will improve OER kinetics and activity for water splitting due to their inherent high electro-catalytic surface area, large aspect ratios (length-to-width ratio) and facile electron transport channeled by the 1D nanorod arrays.6 Consequently, in the present study, aided by our theoretical first principles electronic structure and reaction energy calculations, we have explored reduced noble metal containing 1D nanorod morphology of F substituted earth abundant transition metal oxide based electrocatalyst compositions. The as-synthesized 1D electrocatalyst system exhibit significantly lower charge transfer resistance (Rct) (2.5 Ω.cm2) than benchmark IrO2 (41 Ω.cm2) and other PGM based OER catalysts. In addition, the 1D electrocatalyst system display remarkable activity yielding a current density of ~ 10 mA/cm2 at a low over-potential of ~200mV. The 1D vertical channels of nanorods also provide a facile electron transport contributing to excellent electrochemical OER performance with significantly higher mass activity (40 Ag-1), turnover frequency (TOF~0.010 S-1) and higher electrochemically active surface area (ECSA~700 m2g-1) than the benchmark IrO2. Further, chronoamperometry tests in 1N H2SO4 exhibit minimal current density loss, indicating good electrochemical stability attesting to the promise of this 1D nanorod morphology of the electrocatalyst system for PEM water splitting. Results of these studies will be presented and discussed. Acknowledgements: Financial support of NSF-CBET grant# 1511390, Edward R. Weidlein Chair Professorship funds, Center for Energy Graduate Student Fellowship and the Center for Complex Engineered Multifunctional Materials (CCEMM), University of Pittsburgh is acknowledged.