High-index crystal plane of ZnO nanopyramidal structures: Stabilization, growth, and improved photocatalytic performance

Highlights: • ZnO pyramidal structures are attainable under an oxygen deficient environment. • Surface-stabilized chemical vapor deposition can grow high-index crystal surface. • The surface property was studied by water splitting and electrostatic potential. • Pyramidal ZnO surface shows ambipolar semiconducting properties. • Photocatalytic performances are improved by 73% on the pyramidal surfaces. While the low-index planes of Wurtzite ZnO, such as $\left\{0001\right\}$ and $\left\{10\overline{1}0\right\}$ are well-understood, the high-index crystal surfaces have not yet been thoroughly researched despite possessing structural characteristics that make them suitable for many important surface chemistry processes. The high surface energy of high-index ZnO crystal surfaces makes synthesis challenging to achieve due to their instability during crystal growth. In this work, we present a combined experimental and theoretical analysis of growth and photocatalytic activity of ZnO high-index crystal facets. Density functional theory calculations are performed to determine the thermodynamic conditions necessary to stabilize the high-energy semi-polar $\left\{11\overline{2}2\right\}$ facets of pyramidal ZnO nanostructures grown via chemical vapor deposition (CVD). The photocatalytic properties of as-synthesized nanopyramidal structures for water splitting applications showed a 73% improved photocatalytic performance compared to CVD-grown hexagonal ZnO nanorods with dominating low-index $\left\{10\overline{1}0\right\}$ facets.