Hydroxide-based high entropy metal organic framework for oxygen evolution reaction (OER) and the role of nucleophilicity in OER Biswajit Bhattacharya, Arkendu Roy, Sourabh Kumar, Tilmann Hickel, Franziska Emmerling Bundesanstalt für Materialforschung und -prüfung, Berlin, Germany The energy crisis becomes more prominent in higher altitude countries like Germany, with higher annual energy demand. 1 Thus, the generation of higher energy density fuel like hydrogen from renewable resources become the only way to solve the zero-emission energy system while avoiding the expensive batteries as an energy storage system. Therefore, water electrolysis cells to produce hydrogen and oxygen by storing of solar/wind energy in chemical bonds is a fruitful alternative for renewable and long-term energy generation. Thus, designing inexpensive water-splitting electrocatalyst material becomes a field of research of utmost importance. 2 High entropy metal hydroxide organic frameworks (HE-MHOFs) are composed of high entropy hydroxide layer inside MOFs, resulting in a high degree of structural complexity and diversity than conventional MOFs. 3 The concept of ‘high entropy’ refers to multiple types of metal ions in a near equimolar ratio in the same framework, creating a high degree of disorder and many possible structural configurations. 4 Here, the HE-MHOF successfully synthesized by a conventional solvothermal process, crystallizes in the single phase with significant lattice distortion. A special-quasi-random (SQS) structure was simulated with equimolar compositions (~20% TM = Mn, Co, Ni, Cu and Zn) and a comparison was made with the ICP-AES (inductively coupled plasma atomic emission spectroscopy), XANES (X-ray absorption near edge structure) and XAFS (X-ray absorption fine structure) observations. Further, the elemental mapping (Energy dispersive Spectroscopy) of HE-MHOF shows the presence of all five different metals in the same crystallite to substantiate the ‘high entropy’ state of the MOF. The HE-MHOF offers improved thermal stability than mono-metallic MHOF and exhibit unique properties compared to traditional monometallic (Ni 2+ ) MOF variants. Firstly, to elucidate the effect of the multi-metallic system on the catalytic performance, we have performed density functional theory (DFT) calculations to investigate pre-redox cycles and the HE-MHOF as an electrocatalyst for oxygen evolution reaction (OER) due to its special high entropy hydroxide layered structure and electronic properties. Our DFT results have examined the traditional proton- coupled electron transfer (PCET) steps involving the single transition-metal site. The scrutiny of d-band centers and their behaviour in catalytic upgradation is investigated with density of states (DOS) analysis. It exhibits outstanding performance towards oxygen evolution reaction (OER) comparable to the experimental findings, which is also comparable to state-of-the-art OER catalysts based on precious metals such as iridium oxide and platinum carbon. References 1. B. J. Van Ruijven, E. De Cian and I. Sue Wing, Nat Commun , 2019, 10 , 2762. 2. Z. W. Seh, J. Kibsgaard, C. F. Dickens, I. Chorkendorff, J. K. Nørskov and T. F. Jaramillo, Science , 2017, 355 , eaad4998. 3. S. Xu, M. Li, H. Wang, Y. Sun, W. Liu, J. Duan and S. Chen, J. Phys. Chem. C , 2022, 126 , 14094–14102. 4. Y. Ma, Y. Ma, Q. Wang, S. Schweidler, M. Botros, T. Fu, H. Hahn, T. Brezesinski and B. Breitung, Energy Environ. Sci. , 2021, 14 , 2883–2905.
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