A vast amount of waste heat is generated annually from the industrial and power sectors, estimated at approximately 391 TWh, equivalent to about 35% more than the UK’s total annual electricity demand. It is therefore imperative to utilize efficiently all possible waste heat sources which may be classified according to their temperatures as; low grade (ambient–250°C), medium grade (250–500°C), and high grade (> 500°C). With appropriate technologies, a large proportion of this waste energy could potentially be recovered for useful applications. In this context, thermal energy storage (TES) technologies provide the best opportunities to recover waste heat at various temperatures for long-term storage and application. The potential of thermochemical energy storage (TCES) materials such as magnesium hydroxide, Mg(OH)2, has been established but it has a relatively high dehydration temperature thus limiting its potential for medium-temperature heat storage applications that account for a vast proportion of industrial waste heat. To this end, samples of doped Mg(OH)2 with varying proportions (5,10,15, and 20 wt%) of potassium nitrate (KNO3) have been developed and characterized for evaluation. The results showed that the doped Mg(OH)2 sample with 5 wt% KNO3 achieved the best outcome and was able to lower the dehydration temperature by about 23˚C with an increase of 6% in the energy storage capacity. The results also showed good surface topology and thermal stability in the non-isothermal test conducted on the sample and therefore appear to have the potential for medium heat storage applications ranging from 293˚C to 400˚C.