Ethan Demeter — 2010-11 Fellow
Meeting the energy demands of an ever-growing population, while also weaning ourselves from fossil fuel power generation, is one of the most daunting challenges for the coming decades. This challenge presents the need for developing efficient, clean alternative energy sources; one such technology is renewable energy powered water electrolysis; electrochemically producing hydrogen and oxygen from water. In addition to enabling aspects of the hydrogen economy by efficient hydrogen production, the oxygen that is co-produced would enable CO2 capture applications that utilize oxygen in oxycombustion or gasification-based power generation systems. Current water splitting technologies are hindered by high electrode overpotentials associated with oxygen evolution, and the stability of the electrodes in the highly oxidizing conditions. Our proposed work will focus on the development of a new oxygen evolution electrode that is more efficient, more stable and more cost effective than existing Pt-based carbon electrodes. We propose the use of porous, decorated metal electrodes as a means of reducing the oxygen evolution overpotential, and thus, making water splitting a more realistic clean energy alternative.
For the electrolysis reactions of water shown above to occur, the applied cell potential must exceed 1.23 V, the standard electrode potential for oxygen evolution relative to the hydrogen electrode. These two reactions are coupled, and both occur at the same rate. However, practical cell potentials to split water far exceed this value of 1.23 V due to the large overpotentials associated with the oxygen evolution reaction. In other words, hydrogen production by electrolysis is limited by and is inefficient because of the oxygen evolution reaction that occurs on the other side of the cell. Significantly reducing the oxygen evolution overpotential would reduce the amount of energy required for water splitting, potentially making it a viable method to produce hydrogen for the burgeoning hydrogen economy. Viable anode electrodes must have high surface areas of efficient electrocatalysts that are oxidatively stable and electrically conductive. Carbons, although cheap and conductive are readily oxidized to CO2, limiting the life of the electrodes. Our approach will combine recent advancements in solid oxide fuel cell electrode synthesis with recent oxygen evolution electrocatalyst design from our group.
The key factor to stability is avoiding the use of carbon as an electrical support in the electrode structure. To avoid the use of carbon, we will use metallic nickel to form the support for the catalyst system. The Ni mesh is a cheap material, but it is not the ideal catalyst for oxygen evolution; therefore, we have designed a method of decorating metallic nickel mesh with our anode catalysts that combines the stability of the metallic support with our binary metal oxide elecrocatalyst to enhance the efficiency of the electrode for oxygen evolution.
Recent work in our lab has utilized the evaporation induced self assembly synthesis to produce iron-doped nickel oxide oxygen evolution electrocatalysts with surface areas in the range of 10-30 m2/gm. These materials are very cost-effective compared to platinum-based electrodes. More interestingly, we observed a 3-fold increase in the efficiency of the electrocatalysts (Figure 2) with about 5% Fe doping. These experiments were performed on carbon paper supported electrodes, which are known to have long-term stability problems due to oxidative corrosion of the carbon. Furthermore, we were not able to show whether further increases in efficiency are possible by supporting the mesoporous oxide on a porous support. Our proposal is to integrate this synthesis into the decoration of the metal mesh electrode structures previously described to create highly efficient, stable, cost effective oxygen evolution electrodes.
The results from this research would have broad impact beyond oxygen evolution anodes for water splitting. The technology of these electrodes could impact energy storage applications, chlorine production and fuel synthesis applications in addition to enabling the hydrogen economy.