Energy production relocated to promoting renewable energy requires an intermediate means of storage of surplus production to stabilize the electrical grid during peak demand or low energy production. To initiate this energy transition, it is first necessary to develop these technologies for the conversion and storage, make it reliable, easily integrated into the desired environment and especially to offer competitive hybrid means both from a standpoint of performance from an economic standpoint. This book will describe the approaches and scientific and technological advances in this area, partly on monofunctional coupled devices and secondly on bifunctional materials that provide both functions of conversion and storage of energy the molecular level.