The generation of clean and sustainable hydrogen via advantageous proton exchange membrane (PEM) based water electrolysis is hitherto considered as one of the most efficient and reliable technologies among all other conventional hydrogen production approaches¹. However, commercial development of this technology has been largely constrained due to the need for highly expensive and environmentally scarce platinum group metal (PGM) based electro-catalysts such as Pt, RuO₂, and IrO₂ which exhibit excellent electro-catalytic performance towards energy intensive and sluggish oxygen evolution reaction (OER) in PEM water electrolysis^{2, 3}. Therefore, identification, synthesis and development of novel reduced noble metal containing electro-catalysts, exhibiting remarkable electro-catalytic activity and robust long term electrochemical stability similar/superior to state-of-the art OER electro-catalyst - IrO₂ in highly acidic operating conditions of OER is highly desirable. This will lead to capital cost reduction of PEM water electrolyzer cells creating a path towards commercialization. In line with this objective, utilizing theoretical first principles approaches, we have engineered anionic fluorine (F) doped solid solution of MnO₂ and IrO₂, denoted as (Mn_1-xIr_x)O₂:10F (x=0.2, 0.3, 0.4) as an efficient OER electrocatalyst system, exhibiting lower onset potential and higher current density than the state-of-the art IrO₂ and other previously reported systems for PEM water electrolysis⁴. The electrochemical characterization of the as-prepared electro-catalysts has been carried out in a three-electrode configuration system, using 1N sulfuric acid (H₂SO₄) solution as a proton source as well as the electrolyte.

As shown in Fig. 1 (a), the as-synthesized electro-catalysts (Mn_1-xIr_x)O₂:10F (x=0.2, 0.3 and 0.4) demonstrate notable electro-catalytic performance with a lowest reported onset potential to date of ~ 1.35 V (vs. NHE), ~ 80 mV lower than that of IrO₂ ( ~1.43 V vs. NHE). The (Mn_1-xIr_x)O₂:10F (x=0.2, 0.3 and 0.4) electro-catalysts also exhibit superior electro-catalytic activity (measured at ~1.45 V vs. NHE) i.e. ~ 15 fold higher current density (for x = 0.3 and 0.4) compared to the standard IrO₂ (Fig. 1a). This superior electrochemical performance of as-prepared (Mn_1-xIr_x)O₂:10F electro-catalysts is attributed to the lower charge transfer resistance (R_ct, determined from the diameter of the semi-circle in the low frequency region of the EIS plot, Fig. 1b) and beneficial electronic structure modification upon the introduction and generation of F-doped solid solution. In addition, chronoamperometry tests conducted in 1N H₂SO₄ solution at ~1.45 V (vs. NHE) for 24 hours displayed minimal loss in current density, indicating good electrochemical stability of the as-prepared electro-catalyst.

In summary, the present electro-catalyst system with ~80% reduction in noble metal content, displays significantly much higher electro-catalytic performance than the state-of-the art IrO₂, suggesting the favorable reduction in the overall capital cost of PEM based water electrolyzer and thus, contributing to efficient and economic hydrogen production. Results of these studies will be presented and discussed.

References:

1. M. K. Datta, K. Kadakia, O. I. Velikokhatnyi, P. H. Jampani, S. J. Chung, J. A. Poston, A. Manivannan and P. N. Kumta, Journal of Materials Chemistry A, 2013, 1, 4026-4037.
2. A. T. Marshall and R. G. Haverkamp, Electrochimica Acta, 2010, 55, 1978-1984.
3. S. Ghadge, M. Chavan, A. Divekar, A. Vibhandik, S. Pawar and K. Marathe, Separation Science and Technology, 2015, 50, 365-372.
4. S. D. Ghadge, P. P. Patel, M. K. Datta, O. I. Velikokhatnyi, R. Kuruba, P. M. Shanthi and P. N. Kumta, RSC Advances, 2017, 7, 17311-17324.

Acknowledgements:

Financial support of NSF-CBET grant# 1511390, Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM) is gratefully acknowledged.