Utilising the intrinsic characteristics of blind-hole nanoporous anodic alumina for blue energy

Abstract. Osmotic energy generation is a promising renewable energy technology that converts the osmotic potential between two saline solutions of different concentration into electricity. Ion exchange membranes (IEMs) have gained attention as promising materials, but the high ionic resistance and low power output have prevented IEMs from achieving satisfactory performances for real-life applications. Nanoporous anodic alumina (NAA) is a promising platform material to develop IEMs with precisely tailored properties because of its intrinsic ionic current rectification (ICR) properties. NAA provides new venues to control the transport of ions through its barrier oxide layer, to generate current associated with the selective flow of ions across its nanochannels. This study explores the capability of blind-hole NAA membranes for osmotic energy generation. Featuring a surface area of 13.4 mm², NAA membranes demonstrate the ability to produce a power density output of approximately 2.8×10⁻⁴ W m⁻² under conditions of a 105-fold salinity ratio at pH 3 in a CaCl₂ electrolyte solution. This achievement is coupled with a notable efficiency rate of 7%.