Rational Design of Diamond Electrodes

ConspectusDiamond electrodes stepped onto the stage in the early 1990s for electroanalytical applications. They possess the features of long-term chemical inertness, wide potential windows, low and stable background currents, high microstructural stability at different potentials and in different media, varied activity toward different electroactive species, reliable electrochemical response of redox systems without conventional pretreatment, high resistance to surface fouling in most cases, and possibility of forming composites with different components such as other carbon materials, carbides, and oxidizes. Most diamond electrodes are prepared in microcrystalline or nanocrystalline form using chemical vapor deposition techniques. Starting from diamond films and diamond composites, numerous nanostructured diamond electrodes have also been produced. The features of diamond electrodes are therefore heavily dependent on the growth conditions and post-treatment procures that are applied on diamond electrodes such as introduced dopant(s), surface termination(s), surface functional group(s), added components, and final structure(s). Numerous applications of diamond electrodes have been explored in the fields of electrochemical sensing, electrosynthesis, electrocatalysis, electrochemical energy storage and conversion, devices, and environmental degradation.This Account summarizes our strategies to design different diamond electrodes, including diamond films, diamond composites, as well as their nanostructures. With respect to diamond films, the modulation of their dopant(s) and surface termination(s) as well as the attachment of functional modifier(s) onto their surface are discussed. Electrochemical hydrogenation and oxygenation of diamond electrodes are detailed at an atomic scale. As the examples of designing diamond electrodes at a molecular scale, photochemical and electrochemical attachment of modifier(s) onto diamond electrodes are shown. Moreover, electrochemical grafting of diazonium salts is proposed as a new technique to identify hydrogenated, hydroxylated, and oxygenated terminations of diamond electrodes. The introduction of additional component(s) into a diamond film to form diamond composites is then overviewed, where a hydrogen-induced selective growth model is proposed to elucidate the preparation of diamond/β-SiC composites. Subsequently, the production of various diamond nanostructures from diamond films and composites by means of top-down, bottom-up, and template-free approaches is shown. Electrochemical application examples of diamond electrodes are overviewed, covering direct electrochemistry of natural Cytochrome c on a hydroxylated diamond surface, sensitive electrochemical DNA biosensing on tip-functionalized diamond nanowires, and construction of high-performance supercapacitors using diamond electrodes and redox electrolytes. Our diamond supercapacitors, also named battery-like diamond supercapacitors or diamond supercabatteries, are highlighted since they combine the features of supercapacitors and batteries. Future perspectives of diamond electrodes are outlined, ranging from their rational design and synthesis to their electrochemical applications in different fields.