469355 Highly Active Robust F Doped Transition Metal Oxide Based Solid Solution Electro-Catalyst for Acidic Medium Oxygen Evolution Reaction in PEM Based Water Electrolysis

Wednesday, November 16, 2016: 4:41 PM
Continental 1 (Hilton San Francisco Union Square)
Shrinath Ghadge1, Prasad P. Patel2, Moni Kanchan Datta3, Oleg Velikokhatnyi4, Prashanth Jampani3 and Prashant Kumta5, (1)Chemical Engineering, University of Pittsburgh, Pittsburgh, PA, (2)Department of Chemical & Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA, (3)Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, (4)Center for Complex Engineered Multifunctional Materials, University of Pittsburgh, Pittsburgh, PA, (5)Bioengineering, University of Pittsburgh, Pittsburgh, PA

           The vast consumption of fossil fuels for meeting the energy demand has led to major unsustainable environmental concerns due to excessive greenhouse gas emissions warranting the identification and development of clean non-carbonaceous energy sources.1-5 In this regard, hydrogen has been identified as a clean, non-carbonaceous and potential energy source with superior energy density than currently adopted carbonaceous energy sources for meeting the global energy demand. However, efficient and economic production along with cost-effective storage and distribution of hydrogen utilizing the clean non-carbonaceous approach is of paramount importance before universal adoption of hydrogen as a clean energy source in the impending non-carbonaceous fuel economy. Along these lines, electricity driven water splitting (water electrolysis) is a frontrunner among other clean pollution free approaches for hydrogen production (having low carbon footprint). The commercial development of water electrolysis is thwarted due to the need of expensive and precious noble metals based electro-catalysts (Pt, IrO2) which exhibit excellent electro-catalytic activity and stability for oxygen evolution reaction (OER) in acid assisted proton exchange membrane (PEM) based water electrolysis. Hence, the identification and development of novel reduced noble metal containing electro-catalysts exhibiting excellent electro-catalytic activity and superior long term electrochemical stability similar/superior to state of the art OER electro-catalyst IrO2 in harsh and highly acidic operating conditions of OER, will aid in the reduction of capital cost of water electrolysis cells and thus, its progression towards commercialization.6

          With this aim in mind, exploiting theoretical first principles calculations of the total energies and electronic structures, fluorine doped transition metal (TM) oxide based solid solution electro-catalyst containing significantly lower noble metal content has been identified exhibiting surface electronic structure and electro-catalytic activity similar to that IrO2.The thin films of 10 wt. % F doped (TM1-xZx)O2 (x=0.2, 0.3, 0.4; Z is a noble metal) coated on Ti foil were synthesized and studied as electro-catalyst for OER in acidic media. Fig. 1 shows the SEM micrograph showing the nanoscale architecture of the representative composition (TM0.8Z0.2)O2:10F. Elemental x-ray maps show homogeneous distribution of elements throughout the material without any segregation at specific site.

           Electrochemical characterization of the synthesized electro-catalysts has been carried out in a three-electrode configuration using 0.5 M sulfuric acid (H2SO4) solution as a proton source as well as the electrolyte, Pt wire as counter electrode and Hg/Hg2SO4 as the reference electrode (+0.65 V with respect to normal hydrogen electrode, NHE), with a scan rate of 10 mV/sec and at temperature of 400C. (TM1-xZx)O2:10F (for x = 0.2, 0.3, 0.4) electro-catalysts (total loading = 0.3 mg/cm2) exhibit excellent electrochemical activity for OER with significantly reduced onset potential (~1.35 vs RHE) compared to that of IrO2 (~1.43 vs RHE) (total loading=0.3 mg/cm2). In addition, (TM1-xZx)O2:10F displayed outstanding ~8, ~14 and ~15 fold improved electro-catalytic activity at ~1.45 V (vs RHE) compared to IrO2. Following chronoamperometry test conducted in 0.5 M H2SO4 solution at ~1.55 V (vs RHE) for 24 h, minimal loss in current density as well as excellent long term electrochemical stability was observed for (TM0.8Z0.2)O2:10F, similar to that of IrO2.

           These results show the promise of (TM1-xZx)O2:10F electro-catalyst portending ~80% reduction in noble metal content displaying significantly much higher electro-catalytic activity than IrO2 and superior long term stability. In addition, these results show the promise of the formation F-doped solid solution in improving the electronic, physical, chemical and electro-catalytic properties of the doped TM oxide structures in acidic media. This will aid in significant reduction in the overall capital cost of PEM based water electrolysis for efficient and economic production of hydrogen. The results of these studies will be presented and discussed.

References:

1              Patel, P. P. et al. Nanostructured robust cobalt metal alloy based anode electro-catalysts exhibiting remarkably high performance and durability for proton exchange membrane fuel cells. Journal of Materials Chemistry A 3, 14015-14032 (2015).

2              Patel, P. P. et al. WO3 based solid solution oxide–promising proton exchange membrane fuel cell anode electro-catalyst. Journal of Materials Chemistry A 3, 18296-18309 (2015).

3              Patel, P. P. et al. High performance and durable nanostructured TiN supported Pt 50–Ru 50 anode catalyst for direct methanol fuel cell (DMFC). Journal of Power Sources 293, 437-446 (2015).

4              Patel, P. P. et al. Vertically aligned nitrogen doped (Sn,Nb)O2 nanotubes – Robust photoanodes for hydrogen generation by photoelectrochemical water splitting. Materials Science and Engineering: B 208, 1-14, (2016).

5              Patel, P. P. et al. Nitrogen and cobalt co-doped zinc oxide nanowires – Viable photoanodes for hydrogen generation via photoelectrochemical water splitting. Journal of Power Sources 299, 11-24, (2015).

6              Datta, M. K. et al. High performance robust F-doped tin oxide based oxygen evolution electro-catalysts for PEM based water electrolysis. Journal of Materials Chemistry A 1, 4026-4037, (2013).

Acknowledgements:

           The authors gratefully acknowledge the financial support of NSF-CBET grant# 1511390. The authors also acknowledge the Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM) for partial support of this research.

 


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