A cation reduction device according to the disclosure includes a photocatalytic cell containing an electrolyte containing a first cation and photocatalyst particles, in which the electrolyte and the photocatalyst particles reduce the first cation to a second cation by photocatalytic activity of the photocatalyst particles generated by receiving light, and a pH of the electrolyte is within a pH range in which a zeta potential of the photocatalyst particles is 0 mV or higher.

An apparatus for synthesizing urea comprises an ammonia source, a urea synthesis unit, wherein the ammonia source is connected to the urea synthesis unit via a reactant conduit, and an ammonia gas turbine, wherein the ammonia source is connected to the ammonia gas turbine via a fuel conduit and the ammonia gas turbine is connected to the urea synthesis unit via a steam conduit.