Experimental study of different shaped nanopores in a porous silicon cathodic exchange membrane for reverse electrodialysis

In the context of blue energy harvesting in a reverse electrodialysis cell, the shape of the nanopores of the ion exchange membrane is a key parameter for its efficiency. In this work, the impact of porous silicon pore topology is investigated using numerical simulation and the results are validated using experimental tests. The initial numerical simulations confirms that smaller pore radii imply better selectivity, while osmotic current increases for larger pores. Based on these results, three topologies are selected for an in depth study: conical pore, pencil-shaped pore with 70:30 ratio (i.e. 70% of the length being cylindrical and the rest conical) and pencil-shaped pore with a 50:50 ratio. The numerical simulations show that, although the conical pore offers a better selectivity and membrane potential, the corresponding internal resistance increases and therefore reduces the current flow. The Membranes with pencil-shaped pores are a trade-off between the excellent selectivity of conical pores and the higher current flow of cylindrical pores. Both membranes are then tested experimentally. Membranes with conical pores give maximum power densities of 1.8 𝑚𝑊/𝑚² (four to five times higher than those with cylindrical pores). Membranes with pencil-shaped pores show similar selective performance and slightly lower electrical resistance.