This work is primarily focused on indium sulfide (β-In 2 S 3 ) and cobalt (Co)-doped β-In 2 S 3 nanoflakes as photoanodes for water oxidation. The incorporation of cobalt introduces new dopant energy levels increasing visible light absorption and leading to improved photo-activity. In addition, cobalt ion centers in β-In 2 S 3 act as potential catalytic sites to promote electro-activity. 5 mol% Co-doped β-In 2 S 3 nanoflakes when tested for photoelectrochemical water splitting exhibited a photocurrent density of 0.69 mA cm −2 at 1.23 V, much higher than that of pure β-In 2 S 3 . © The Royal Society of Chemistry.