(400d) Next-Generation Microstructured Water-Splitting Devices

Expanding the electrochemical hydrogen generation capacity in our current energy ecosystem can allow for the incorporation of a larger share of renewables into the grid. Although efficient electrolyzers are commercially available, their high cost has precluded their deployment. Significant simplifications of electrolyzers’ design and operation can lead to more practical solutions for water splitting and ultimately propel their large scale society utilization. Here, we demonstrate two proof-of-concept electrolysis devices which differ significantly from their conventional counterparts. The first system is an electrolyzer that balances fluid mechanic forces in order to maintain the evolved oxygen and hydrogen gas streams separated even without the implementation of a membrane. As the system can operate membrane-less, the electrolysis efficiency can be enhanced; operating current densities can reach levels above 300 mA/cm²; and the water splitting process can take place under a broad range of electrolytes and across the pH scale. This allows for the incorporation of inexpensive and earth-abundant catalyst materials that are only stable under mild pH conditions. The second device directly splits water from humid ambient air streams. In this device, water molecules are absorbed in an ionomer thin film (Nafion^®), and then react at the interface between the ionomer and the catalyst to generate hydrogen and oxygen streams. As all of the processes take place inside the ionomer, the device is able to operate directly with humid gaseous streams, reaching current densities over 10 mA/cm² without using liquid electrolytes or liquid water feeds. Furthermore, the design simplicity and performance under mild operating conditions of this device can simplify the integration and stable operation of photoactive components, leading to solar-driven water-vapor splitting devices.