Nickel-iron (NiFe) batteries are an appropriate solution for utility-scale energy storage due to a long service life, high tolerance to deep discharge and overcharge and low cost materials with low toxicity. However, a parasitic hydrogen evolution reaction on the iron electrode contributes to low charging efficiencies. In the current study an in situ scanning vibrating electrode technique (SVET) has been used to measure the volume of hydrogen evolved upon charging. The technique allows the characterisation of current density distributions over the electrode surface when immersed in KOH (30% w/v solution) electrolyte. The technique has been verified by comparison with current measurements and a traditional volumetric analysis technique. Furthermore, additives of S and LiOH have been made to the electrolyte to determine any change in the volume of hydrogen evolved where effectiveness at reducing hydrogen evolution was such that S > LiOH > no additive.