Combined system for the production of hydrogen, oxygen and segregated and sequestered carbon dioxide; the combined system comprises: an electrolysis plant configured to receive water and electrical energy (E 1, E 2) as an input and supply hydrogen and oxygen in gaseous form as an output; an electricity generation plant which is equipped with an electrical generator that generates at least part of the electrical energy (E 2) used by the electrolysis plant and a thermal engine that drives the electrical generator and comprises: an intake duct; an exhaust duct; and a recirculation duct connecting the exhaust duct to the intake duct to recirculate the exhaust gases produced by the combustion; a feed duct that sends the oxygen generated by the electrolysis plant to the intake duct of the thermal engine; and an extraction duct configured to draw a portion of the exhaust gases from the exhaust duct of the thermal engine by withdrawing them from the recirculation duct; the combined system is characterised by the fact that it comprises: a first heat exchanger which is arranged along the extraction duct and is configured to cool the exhaust gases to a temperature below a dew point of the gaseous mixture in order to condense the carbon dioxide; a first separator which is arranged along the extraction duct downstream of the first heat exchanger and is configured to separate liquefied carbon dioxide from the non-condensable gases in the exhaust gases; and a recovery duct connecting the first separator to the feed duct in order to introduce into the feed duct the non-condensable gases present in the exhaust gas and extracted from the first separator. an electrolysis plant configured to receive water and electrical energy (E 1, E 2) as an input and supply hydrogen and oxygen in gaseous form as an output; an electricity generation plant which is equipped with an electrical generator that generates at least part of the electrical energy (E 2) used by the electrolysis plant and a thermal engine that drives the electrical generator and comprises: an intake duct; an exhaust duct; and a recirculation duct connecting the exhaust duct to the intake duct to recirculate the exhaust gases produced by the combustion; a feed duct that sends the oxygen generated by the electrolysis plant to the intake duct of the thermal engine; and an extraction duct configured to draw a portion of the exhaust gases from the exhaust duct of the thermal engine by withdrawing them from the recirculation duct; the combined system is characterised by the fact that it comprises: a first heat exchanger which is arranged along the extraction duct and is configured to cool the exhaust gases to a temperature below a dew point of the gaseous mixture in order to condense the carbon dioxide; a first separator which is arranged along the extraction duct downstream of the first heat exchanger and is configured to separate liquefied carbon dioxide from the non-condensable gases in the exhaust gases; and a recovery duct connecting the first separator to the feed duct in order to introduce into the feed duct the non-condensable gases present in the exhaust gas and extracted from the first separator. a first heat exchanger which is arranged along the extraction duct and is configured to cool the exhaust gases to a temperature below a dew point of the gaseous mixture in order to condense the carbon dioxide; a first separator which is arranged along the extraction duct downstream of the first heat exchanger and is configured to separate liquefied carbon dioxide from the non-condensable gases in the exhaust gases; and a recovery duct connecting the first separator to the feed duct in order to introduce into the feed duct the non-condensable gases present in the exhaust gas and extracted from the first separator.