Designing electrochemically reversible H2 oxidation and production catalysts

Abstract

The most energy-efficient electrocatalysts mediate forward and reverse reactions at high rates with minimal overpotential requirements. Such electrocatalytic reversibility is commonly observed for redox enzymes and is an attribute that we have sought to bestow on synthetic molecules to realize highly active and robust catalysts for applications in renewable energy. The recent development of the first synthetic molecular catalysts that reversibly mediate H2 ⇌ 2 H+ + 2e− exploits an enzyme-inspired outer coordination sphere that works in concert with both first and second coordination spheres. In this Perspective, we discuss a series of molecular Ni catalysts for H2 production and oxidation that exhibit electrochemical reversibility. Study of these catalysts allows us to identify important first, second and outer coordination sphere features necessary for efficient conversions of H2 and provides direction for the rational design of electrocatalysts that operate on other small molecules. This Perspective describes how reversible catalysis — a hallmark of enzymes — can be reproduced in synthetic catalysts by rationally designing first and second coordination spheres, as well as amino acid-based outer coordination spheres. We describe this in the context of Ni prototypes for efficient H2 oxidation and evolution.