The concentration distribution of hydroxyl radicals (center dot OH) has a crucial influence on planarization accuracy and efficiency in a photoinduced confined chemical etching system. To elucidate the concentration distribution of center dot OH near the titanium dioxide (TiO2) photoanode, we proposed two in situ strategies with micrometer-scale spatial resolution: the substrate-generation/tip-collection mode of scanning electrochemical microscopy (SECM) and the deposition-etching-stripping method, by which the influence of the scavenger (i.e., glycine) and the apparent thicknesses of confined etching layers were estimated. The developed SECM methodologies provide powerful analytical tools for the screening of photoinduced chemical etching systems as well as further research on confining and etching mechanisms. (c) 2017 Elsevier Ltd. All rights reserved.