(639h) Development of Vertically Aligned Boron-Nitride-Nanopore Membranes for Giant Osmotic Power Generation

Development of Vertically Aligned Boron-Nitride-Nanopore Membranes for Giant
Osmotic Power Generation

Aaditya Pendse¹, Semih Cetindag², Sanjay Behura¹,
Vikas Berry¹, Jerry Shan² and Sangil Kim¹

1.     Department
of Chemical Engineering, University of Illinois, Chicago, IL 60607

2.     Department
of Mechanical & Aerospace Engineering, Rutgers University, Piscataway, NJ
08854

The
use of salinity-gradient power, based on the Gibbs free energy of mixing fresh
and salt water, has been under intensive investigation for clean-energy
harvesting from abundant environmental resources. However, the current reverse
electrodialysis (RED) systems based on polymeric ion exchange membranes (IEMs)
suffer from lower power density (approximately 1-3 W/m²), low
efficiencies, and high membrane cost. A recent experimental study on a membrane
containing a single boron-nitride-nanotube pore showed electric currents as
high as 1.2 nA. Extrapolating this result to a
macroscopic membrane, with a boron-nitride pore density of ~10¹⁰ nanotubes/cm²,
would result in a power density of ~4 kW/m². However, no such
large-surface-area vertically aligned boron-nitride-nanopore (VA-BNNP)
membranes have ever been fabricated.

Here, for
the first time, we demonstrate the power generation performance of macroscopic
VA-BNNP membranes with high nanopore density, up to ~10⁸
pores/cm².   For
the fabrication of VA-BNNP membranes, a thin hexagonal boron nitride (hBN) layer was deposited within the pores (~100 nm) of
anodized alumina substrates by low-pressure chemical vapor deposition.
Cross-sectional scanning-electron-microscope (SEM) images show the hBN layer (~35 nm) was uniformly deposited along the pores
without excessive hBN on the top surface, ensuring
that most pores remained open. In addition, the results of scanning confocal
Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) showed the high
quality of the hBN layers in the AAO pores. We
investigated the power generation of the macroscopic VA-BNNP membranes at different
pH and salinity concentrations. The power generation per unit pore area increased
as the salt concentration and pH increased. The highest power density of the
membrane was up to ~100 W/m² which is two orders of magnitude higher
than that of RED system based on IEMs or even nanofluidic channels. These
findings indicate the great potential of large-area VA-BNNP membranes as
next-generation nanostructured membranes for renewable energy harvesting.