Determining Functional Parameters of Hybrid Catalysts for Sustainable Energy Storage and Conversion Applications

Abstract

Generating global-scale sustainable energy systems and preserving our environment for the future at the same time are the biggest challenges. Therefore, the search for diverse energy sources which will reduce our dependency on fossil fuels leads to immense attention towards sustainable energy storage and conversion devices like metal-air batteries, fuel cells and water splitting devices (photochemical, electrochemical, photoelectrochemical and photovoltaic coupled to electrolyzers). The aforementioned devices involve key reactions like oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR). The energy barrier to overcome these reactions can be reduced by using a catalyst. Therefore, the rational design of catalysts is important as it determines the performance of such devices. Ir and Ru-based oxides are the benchmark electrocatalysts for OER whereas Pt/C is the benchmark catalyst for ORR, HOR and HER. All being precious metals, various transition metal-based catalysts have gained immense attention. Transition metal-based oxides/hydroxides are believed to be potential candidate for OER. Firstly, we have design Co−Ni-Based hybrid oxide−hydroxide flowers as an efficient electrocatalyst for OER. The importance of integrating the hydroxide moieties in the bimetallic oxide has been elucidated. Improving the functionality of a catalyst reduces the overall cost of device production. In this regard, the functionality of NiCo oxide flower is improved by integrating NiCo encapsulated N-doped carbon nanotubes on Ni-Co oxide flowers which show remarkable bifunctional OER and ORR. Further, this work has been extended to trifunctional OER, ORR and HER activity by designing hierarchical one-dimensional (1D)-two-dimensional (2D) heteroatom-doped carbon nanostructure on the oxide support. iii Multimetallic systems improve the OER performance by improving intrinsic activity. Therefore, trimetallic Co, Ni and Mn-based oxide-hydroxide hybrids have been explored for OER and detailed investigation on the mechanism has been carried out. The importance of electronic modulation via incorporating a third element (Mn) on the bimetallic Co-Ni oxide-hydroxide hybrid has been highlighted. Finally, we have design modified hematite by employing possible ways to improve its photoelectrochemical water splitting performance and the importance of various modification on the water-splitting performance have been investigated. We believe that the present work can provide a basic understanding of the parameters required to design efficient catalysts for various sustainable energy storage and conversion devices.