The recent advancements in key materials including reactants and catalysts employed in solid-gas

gasgas

and liquid-gas solar thermochemical energy storage(TCES) systems are reviewed. The thermochemical properties of reactants such as carbonates

hydroxides

metal hydrides

metal oxides

organics

and ammonia are examined. The research status of the modification of these reactants

new material development

and catalyst improvement are also discussed. At present

the reactant materials suitable for solar TCES exhibit various deficiencies in terms of cyclic stability

reactivity

conversion rate

energy storage density

cost or safety

which hinder the commercial viability of solar TCES technology. To further enhance the maturity of solar TCES technology

it is imperative to develop advanced composite materials on the basis of known thermochemical reaction systems

improve novel efficient catalysts

and broaden demonstration application scenarios and scales in the future.The key materials should endow TCES systems with high energy storage density

more robust cyclic stability

and rapider reaction kinetics. It is preferred that they are readily available

non-corrosive

and non-toxic and more costeffective.