An improved variation of highly active/durable O -evolving LaTiO N powder-based photoelectrode has been fabricated by pre-cleaning the powder with mild polysulfonic acid and by homogeneous deposition of CoO co-catalyst aided by microwave annealing. The treatment in aqueous solution of poly(4-styrene sulfonic acid) results in removal of surface LaTiO N layers, forming fine pores in the crystallites. The CoO co-catalyst by microwave deposition in Co(NH ) Cl /ethylene glycol homogeneously covers the particle surface. The LaTiO N powder is fabricated into particle-transferred electrodes on Ti thin film supported on solid substrate. The modified LaTiO N grains on the electrode serve as a highly active O -evolving photoanode achieving 8.9 mA cm of the photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) in 0.1 m NaOH (pH 13) under solar-simulator irradiation Airmass 1.5 Global (AM 1.5G). The activity has been much improved, compared with conventional LaTiO N treated in mineral acid or with CoO deposited by impregnation. The new electrode also exhibits better durability in fixed-potential chronoamperometric tests under AM 1.5G irradiation.