Electrochemistry of Nanocomposite Materials for Energy Conversion

Energy is the most relevant technological issue that the world experiences today, and the development of efficient technologies able to store and convert energy in different forms is urgently needed. The storage of electrical energy is of major importance and electrochemical processes are particularly suited for the demanding task of an efficient inter-conversion. A potential strategy is to store electricity into the chemical bonds of electrogenerated fuels, like hydrogen and/or energy-dense hydrocarbons. This conversion can be accomplished by water splitting and CO2 electrolysis. In this context, are herein presented three different electrochemical approaches towards water and CO2 reduction. In Chapter 1 is reported a novel class of nanostructured electrocatalysts, MWCNTs@Pd/TiO2, able to efficiently reduce water at neutral pH. Multi-walled carbon nanotubes, Pd nanoparticles and titanium dioxide are mutually integrated within the nanocomposites, whose electrocatalytic properties are thoroughly investigated and optimized. By electrochemical methods it is rationalized the effect of each building block on the overall activity, which originate from the synergic cooperation of the three units. In Chapter 2 is presented an electrochemical study of MWCNTs@CeO2, a noble-metal free electrocatalyst with a similar architecture to MWCNTs@Pd/TiO2. The electroreduction of CO2 has often the drawbacks of a poor selectivity and high energy losses for the high overpotential required to drive the reaction. However, detailed studies of MWCNTs@CeO2 highlights the possibility to convert CO2 to formic acid at very low overpotential and with a high selectivity. A reaction mechanism that involves the participation of surface hydride species and the CeO2 shell is proposed. Finally, in Chapter 3 is presented a photo-electrochemical approach to hydrogen production. Solar energy is converted to hydrogen via water reduction on the surface of a catalyst-free, oxide-protected solar cell. The large solar-to-hydrogen activity of the photocathode assembly has been explained by a combination of experimental and theoretical studies.