Designing Janus catalysts for renewable energy-relevant bifunctional small molecule activation

Abstract

In the current era, harvesting sustainable energy is a prime sustainable goal for the continuous growth of human civilization without any adverse effect on the surrounding atmosphere. The intermittent nature of renewable energy resources has posed serious questions about their potential to provide a reliable flow of continuous energy. A strategic conversion of renewables to chemical energy can offer the leeway for a facile energy transduction process where renewables will be converted into chemical bonds in the first step before their need-based conversion to readily usable electricity or other forms of energy. In this context, two compatible redox couples, H₂O ⇌ H₂ and H₂O ⇌ O₂, have emerged as the prime contenders for small molecule-based energy conversion due to their natural abundance and relatively well-known chemistry. A plethora of synthetic catalysts have been designed to date that can trigger H₂ production, H₂ oxidation, water oxidation, and O₂ reduction. Typically, all these catalysts function independently and must be assembled together for a fully functional setup that can consistently convert renewables to electric energy. This assembly will be practically more useful if bifunctional catalysts, which can execute more than one reaction, can be included. In this review, we have highlighted the evolution of two major classes of such bifunctional or Janus catalysts that can function in H₂ production/water oxidation and O₂ reduction/water oxidation in tandem with the application of the appropriate energy source. The specific design of such catalysts involves the strategic incorporation of dopants and lattice defects on specific metal oxide or metal phosphide templates. Such modulation of the surface morphology is key for developing active heterogeneous Janus catalysts. In this review, we have summarized the different approaches for generating and studying such Janus catalysts, as they will lay the foundation for an efficient, economical, and eco-friendly pathway for sustainable energy usage with the rational assembly of energy converting and storage devices.