Earth-Abundant and Precious Group Metal-Free Electrocatalysts for Hydrogen Evolution Reaction (HER) in Proton Exchange Membrane (PEM) Based Water Electrolysis (2020)

Generation of clean and sustainable hydrogen is critical for heralding the much touted hydrogen economy. Water electrolysis has been considered a favorable option for clean hydrogen production. Furthermore, acid mediated proton exchange membrane (PEM) based water electrolysis is considered one of the most efficient and reliable technologies among all existing conventional hydrogen production approaches 1-7 . To achieve the desired efficiency and reliability, it is imperative to identify high performance and earth-abundant electrocatalysts for expediting the hydrogen evolution reaction (HER). In the present work, utilizing the density functional theory (DFT) based calculations for rationalizing the thermodynamics and reaction kinetics, we have identified and synthesized the platinum group metal (PGM)-free, transition metal non-oxide (TMN) based electrocatalysts for acidic HER. Based on the DFT calculations, the as-synthesized TMN electrocatalyst compositions reveal optimized hydrogen adsorption free energies (ΔG H * ) and beneficial modification of the surface electronic structures, offering excellent charge transfer kinetics, lower activation polarization, higher wettability ( Fig. 1 ), and superior electrocatalytic activity for HER. Additionally, the highly active electrocatalyst compositions display excellent long term electrochemical HER stability in acidic media, without major degradation in current density. The system therefore, has propensity for displaying promising prolonged HER performance with excellent structural robustness and mechanical integrity. The experimental results are ably supported by our DFT calculations which further reveal that introducing suitable dopants into the TMN compositions result in optimized electronic structures that reduce the reaction barriers. Putatively, the system therefore offers improved electrocatalytic activity for HER comparable to state-of-the-art Pt/C. Consequently, the as-synthesized PGM-free electrocatalysts due to their superior electrochemical performance can be considered as potential HER candidates, highly critical for the development of PGM-free, earth-abundant electrocatalysts for PEM based water splitting. Results of this study will be presented and discussed. Acknowledgements: Financial support of NSF-CBET grant# 1511390, Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM) is acknowledged. References: 1. Ghadge, S. D.; Velikokhatnyi, O. I.; Datta, M. K.; Shanthi, P. M.; Tan, S.; Damodaran, K.; Kumta, P. N., Experimental and Theoretical Validation of High Efficiency and Robust Electrocatalytic Response of One-Dimensional (1d) (Mn,Ir)O2:10f Nanorods for the Oxygen Evolution Reaction in Pem-Based Water Electrolysis. ACS Catal. 2019 , 2134-2157. 2. Patel, P. P.; Velikokhatnyi, O. I.; Ghadge, S. D.; Hanumantha, P. J.; Datta, M. K.; Kuruba, R.; Gattu, B.; Shanthi, P. M.; Kumta, P. N., Electrochemically Active and Robust Cobalt Doped Copper Phosphosulfide Electro-Catalysts for Hydrogen Evolution Reaction in Electrolytic and Photoelectrochemical Water Splitting. International Journal of Hydrogen Energy 2018, 43 , 7855-7871. 3. Patel, P. P.; Velikokhatnyi, O. I.; Ghadge, S. D.; Jampani, P. H.; Datta, M. K.; Hong, D.; Poston, J. A.; Manivannan, A.; Kumta, P. N., Highly Active Robust Oxide Solid Solution Electro-Catalysts for Oxygen Reduction Reaction for Proton Exchange Membrane Fuel Cell and Direct Methanol Fuel Cell Cathodes. Int. J. Hydrogen Energy 2017, 42 , 24079-24089. 4. Ghadge, S. D.; Patel, P. P.; Datta, M. K.; Velikokhatnyi, O. I.; Kuruba, R.; Shanthi, P. M.; Kumta, P. N., Fluorine Substituted (Mn,Ir)O2:F High Performance Solid Solution Oxygen Evolution Reaction Electro-Catalysts for Pem Water Electrolysis. RSC Adv. 2017, 7 , 17311-17324. 5. Ghadge, S. D.; Patel, P. P.; Datta, M. K.; Velikokhatnyi, O. I.; Shanthi, P. M.; Kumta, P. N., First Report of Vertically Aligned (Sn, Ir) O2: F Solid Solution Nanotubes: Highly Efficient and Robust Oxygen Evolution Electrocatalysts for Proton Exchange Membrane Based Water Electrolysis. Journal of Power Sources 2018, 392 , 139-149. 6. Ghadge, S. D.; Velikokhatnyi, O. I.; Datta, M. K.; Kumta, P. N. In Influence of Composition and Nano-Scale Morphology on Enhancing the Acid Mediated Oxygen Evolution Electrocatalysis of Earth Abundant and Low Pgm Containing Transition Metal Oxide Solid Solution Oxide Anodes , 2019; The Electrochemical Society: pp 1725-1725. 7. Ghadge, S. D.; Velikokhatnyi, O. I.; Datta, M. K.; Kumta, P. N. In Ultra-Low Noble Metal Containing One-Dimensional Nanorods: High Performance Oer Electrocatalyst for Acid Mediated Pem Based Water Electrolysis , 2019; The Electrochemical Society: pp 1434-1434. Figure 1