In Situ Magnetic Alignment of a Slurry of Tandem Semiconductor Microwires Using a Ni Catalyst

Abstract Slurries of semiconductor particles individually capable of unassisted light‐driven water‐splitting are modeled to have a promising path to low‐cost solar hydrogen generation, but they have had poor efficiencies. Tandem microparticle systems are a clear direction to pursue to increase efficiency. However, light absorption must be carefully managed in a tandem to prevent current mismatch in the subcells, which presents a possible challenge for tandem microwire particles suspended in a liquid. In this work, a Ni‐catalyzed Si/TiO₂ tandem microwire slurry is used as a stand‐in for an ideal bandgap combination to demonstrate proof‐of‐concept in situ alignment of unassisted water‐splitting microwires with an external magnetic field. The Ni hydrogen evolution catalyst is selectively photodeposited at the exposed Si microwire core to serve as the cathode site as well as a handle for magnetic orientation. The frequency distribution of the suspended microwire orientation angles is determined as a function of magnetic field strength under dispersion with and without uplifting microbubbles. After magnetizing the Ni bulb, tandem microwires can be highly aligned in water under a magnetic field despite active dispersion from bubbling or convection.