Evaluating the Potential for Hydrogen Production with Donnan-Driven Multi-Ion Exchange Membrane Based Systems

Abstract

Reverse electrodialysis (RED) is a membrane-based electrochemical system used for harvesting salinity gradient energy (2.6 TW) through the mixing of sea and river water at global estuaries[1]. This is accomplished through a series of anion and cation exchange membranes (AEM and CEM), which drive electrical energy production at adjacent redox electrodes. As more membranes are added to the system, the generated potential increases which increases current production. Galvanic operation of RED for electricity production has been demonstrated, but electrical power density and limiting current density are typically less than 0.2 W/m2 and 10 A/m2 [2]. Here, we propose to produce hydrogen with a RED cell, through operating in an electrolytic mode. This multiple membrane electrolysis process is partially driven by the membranes through their “Donnan-potential”, and partially driven by additional electrical energy input [3-6]. By pushing the RED cell into the electrolytic region, high current density needed for hydrogen production, can be achieved. Here, hydrogen production using an electrolytic RED is evaluated with a varying number of cell pairs (1 to 10) and with acidic, neutral and basic electrolytes at a fixed 10 mA/cm2. Under neutral conditions, the resulting voltage obtained from the RED cell decreased from 2.1± 0.1 V to 1.2±0.2 as the number of cell pairs increased from 1 to 10. In addition, the energy conversion efficiency of the system decreased due to the increase in mixing energy (ΔGmix.) from 130.6 J to 1203.2 J at higher cell pairs. When the cell was operated with an acidic cathode and basic anode, the applied voltage and energy consumption decreased by 45% compared to neutral pH. In addition, the current density achieved was 4x greater at a voltage 1 cell pair. The hydrogen to electrical energy ratio increased from to 100% at 2 mA/cm2 when the number of cell pairs increased from 1 to 10 with neutral electrolytes. This ratio increased by 3x under acid-base electrolytes. Logan, B.E. and M. Elimelech. Nature, 2012. 488(7411): p. 313-319.Zhu, X., He, W., & Logan, B. E. (2015). Reducing pumping energy by using different flow rates of high and low concentration solutions in reverse electrodialysis cells. Journal of Membrane Science, 486, 215-221.Hatzell, M.C., I. Ivanov, R.D. Cusick, X. Zhu, and B.E. Logan. Physical Chemistry Chemical Physics, 2014. 16(4): p. 1632-1638.Nazemi, M., Zhang J., Hatzell M.C., “Harvesting Natural Salinity Gradient Energy for Hydrogen Production through Reverse Electrodialysis (RED) Power Generation”, J. Electrochem. En. Conv. Stor., 2017; DOI: 10.1115/1.4035835.Hatzell, M.C., X. Zhu, and B.E. Logan. ACS Sustainable Chemistry & Engineering, 2014. 2(9): p. 2211-2216.Nazemi, M., Padgett, J., and Hatzell, M.C. (2017). Acid/Base Multi‐Ion Exchange Membrane‐Based Electrolysis System for Water Splitting. Energy Technology.