Metal-layered double hydroxides (LDHs), a family of versatile layered materials recently popular as earthabundant oxygen evolution reaction (OER) catalysts, allow for both metal substitution and interlayer anion exchange without disrupting the two-dimensional (2D) crystal structure, although the ubiquity of carbonate anions is challenging to avoid. Here, we use hydrothermal synthesis in modified solvents with triethanolamine to directly synthesize bulk NiFe LDHs with carbonate, chloride, and sulfate interlayer anions without inert atmosphere protection. Structural characterizations by X-ray diffraction, infrared spectroscopy, and energy-dispersive X-ray spectroscopy confirm the anion composition. Electrochemical characterization shows that LDHs with these three anions display similar OER catalytic performance after surface area normalization, consistent with observed anion exchange to carbonate in alkaline electrolyte under ambient conditions. However, dodecyl sulfate-intercalated NiFe LDHs prepared by anion exchange show enhanced electrocatalytic performance unexplained by surface area and resist carbonate exchange during electrochemical cycling. The synthetic methods developed for carbonate, chloride, and sulfate LDHs also allow direct fabrication of threedimensional high surface area electrodes, but the anion composition of these electrodes does not affect the OER performance after surface area normalization. These results provide new insights on how the interlayer anions in LDH materials influence OER catalytic activity and open a new approach for tuning these catalytic materials.

The solution synthesis of ternary metal oxides is difficult due to the competing hydrolysis of metal ions. There are reports of hydro-/solvothermal growth of nanoparticles, but one-dimensional (1D) nanoarrays are less common. Here, we report an alternative and general strategy to circumvent this challenge by converting the 1D binary metal oxide/hydroxide nanostructures initially grown driven by screw dislocations into ternary oxides. Using the α-GaOOH/α-Ga2O3/ZnGa2O4 wide bandgap transparent conductor materials as a demonstration, we synthesize vertical arrays of high aspect ratio α-GaOOH nanorods (NRs) on conducting substrates with controllable length for the first time using a continuous flow reactor and confirm their growth mechanism to be dislocation-driven. Then the α-GaOOH NR arrays can be converted into porous α-Ga2O3 NR arrays, which can be further converted via a solution method into porous ZnGa2O4 nanotube (NT) arrays due to the Kirkendall effect. This work presents a new and general strategy to prepare 1D nanostructure arrays of various binary and ternary oxides at low cost and large scale, and such facile solution growth and the unique structure of porous ZnGa2O4 NT arrays will facilitate their practical applications.