Thin films of TaOxHy were cathodically electrodeposited from an aqueous solution containing Ta-IPA precursor and KNO3 as a sacrificial agent. It was shown that the deposition resulted from a precipitation reaction triggered by the local change of pH at the surface of working electrode. Combined structural and compositional analysis revealed that during the electrodeposition the oxidation state of tantalum remained constant, Ta(V). The as-deposited films are mesoporous amorphous tantalum oxide hydrate films, which can be converted to either pure Ta2O5 or Ta3N5 by high-temperature annealing in either air (or Ar) or ammonia, respectively. The Ta3N5 electrodes exhibited promising PEC activity for water oxidation. These results open the door for the reduced temperature synthesis of Ta3N5 electrodes on TCO substrates which would allow for efficient overall solar water splitting.