Investigating new sources of renewable energy has been a major focus in the scientific community during the last decade and continues to attract much attention [1]. Photovoltaics -used in the conversion of solar energy to electrical power -are considered a promising technology to meet the requirements of a clean, non-fossil fuel in the future. The photoelectrochemical cell (PEC), utilizing semiconducting surfaces for catalysis, has been intensively studied as a method to generate hydrogen (H 2 ). Novel catalyst compounds, which meet all the essential criteria for a PEC system, i.e. a small energy band gap (E g ) for absorption of visible light, chemical stability for reuse and storage, a negative conduction band potential and an efficient conversion rate, are being investigated. Cu + X 3+ O 2 oxides, where X denotes a transition metal, crystallize in the delafossite structure, have been reported as leading candidates to meet these PEC requirements, primarily as a result of their interesting band-gap modulation, long-term chemical stability, and low-cost [2,3].Mesoporous CuCrO 2 delafossite structures were successfully synthesized by nanocasting methods using KIT-6 as a template. Copper nitrate and chromium nitrate precursors were melted together at 60°C or dissolved in methanol before impregnation into the silica KIT-6 template. After calcination at ~1000°C in Ar, delafossite nanostrutcures were obtained after removal of the silica template by treatment in a NaOH solution. The synthesized mesoporous CuCrO 2 delafossite is a p-type semiconductor with a small band gap of ~1.38 eV. However, the most efficient H 2 generation for this material takes place under irradiation with a wavelength of ~400nm, which is shorter than the expected value (~900 nm). Two potential explanations for this controversial result include (1) the existence of surface defects and (2) a low electronic conductivity in the bulk delafossite, both of which could result in the recombination of photo-generated electrons and holes. To investigate the surface structure and electronic structure of the mesoporous CuCrO 2 , a combination of STEM and EELS was used.A C s -corrected FEI Titan 80/300 TEM/STEM equipped with a Gatan Imaging Filter was used for this study. Bright-field (BF) and dark-field (DF) STEM images were recorded simultaneously to study the crystal structure of the CuCrO 2 delafossite. The fine structures of Cr-L, Cu-L, and O-K edges have been studied to reveal the electronic structure of the material. The oxidation states of Cu and Cr were investigated by EELS. Mesoporous CuCrO 2 samples exposed for different periods of light illumination were evaluated to understand the catalytic stability. In addition, we have also studied bimetallic-doped mesoporous CuCrO 2 to understand how dopants affect the microstructure and photoactivity.The as-synthesized mesoporous CuCrO 2 microstructure is characterized by pore sizes of ~10 nm and an inter-pore spacing of ~17 nm (Figure 1). The mesoporous CuCrO 2 morphology maximizes the solar-to-chemical co...