Energy from streaming potential using nanotechnology

We propose the investigation of electrochemical generation of molecular hydrogen and electrical energy from hydraulic pressure using the streaming potential. Recent theoretical work has indicated that very high conversion efficiencies from the mechanical to the electrical domain can be obtained from this process. In order to obtain such efficiencies, our aim is to investigate and develop micromachined porous membranes with nanosized pores possessing controlled and stable surfaces made of optimized materials. These membranes will be taken up in a larger (hierarchical) structure that will enable both the generation of hydrogen gas and of electricity from the generated streaming potential. The work will be supported by the development of a physicochemical model to describe the mechanism of streaming potential generation in the devices proposed, to interpret and guide experiments. A streaming potential is generated when liquid water is pumped through a porous medium. It is a sustainable way of generating energy, producing no CO2. By coupling the generation of electricity to the in-situ generation of hydrogen in one process, we aim to increase efficiency as well as providing energy in an alternative storable form. Hydrogen is seen as a useful alternative energy carrier, and a hydrogen-based society can be a viable sustainable alternative for the present day fossil energy-based society. To increase the efficiency of the energy generation by the streaming potential, a number of physicochemical and electrochemical issues need to be addressed. The conversion efficiency is conventionally expressed as the ratio of the generated electrical energy over the input of mechanical energy. All mechanical energy that is dissipated in the system without transporting charge is therefore wasted and should be eliminated. The classical answer to this is to scale down the pore cross section, enabling theoretical efficiencies of maximally 7%. However, recent theoretical investigations have indicated that the introduction of liquid slip at the walls may result in a strong further increase of the efficiency, from 7 to 35%. Part of our proposal is therefore the introduction of liquid slip. Another cause of energy loss is a back transport of current through the pore liquid. To eliminate this factor we propose to employ a liquid jet technique, where the liquid will break up in droplets after passing through the pores, to effectively electrically isolate the generator part. As the fluidic format we intend to use micromachined nanoporous membranes, offering massively parallel pores and low flow resistance. Finally, part of our proposal is to study the generation of hydrogen gas in the system, so that a mixture of chemical and electrical energy will be produced. When nanostructured platinum electrodes are used conversion losses can be minimized. Hydrogen generation is of special interest since it is regarded as the prime energy source in a possible future hydrogen economy. In this way the combined, overall energy conversion efficiency may reach values far larger than attainable with conventional techniques. Our research will be based on the use of micro/nanofabrication techniques offered by the MESA+ cleanroom to manufacture membrane devices of the necessary structure and materials. The research team will consist of two Ph.D. students and a full-time cleanroom technician. Existing contacts with the membrane research group of prof. Wessling at Twente University can be exploited for future upscaled production.