Electrochemical system, designed to operate in underpressure with respect to a predefined reference pressure, comprising: o a fuel cell, comprising a cathode inlet (Ce) and a cathode outlet (Cs) which are designed to ensure a flow of oxygen through the fuel cell; o a first fluid supply line (Lad), connecting a first oxygen inlet (Ed) at the reference pressure to the cathode inlet (Ce); o a first fluid discharge line (Led), connecting the cathode outlet (Cs) to a first outlet (Sd); o a pressure reducer, arranged on the first fluid supply line (Lad), and designed to impose a pressure lower than the reference pressure on the oxygen passing through it; o a pump designed to impose an oxygen flow through the first fluid supply (Lad) and discharge (Led) lines, the pump being arranged on the first fluid discharge line (Led), such that when operating in underpressure, the oxygen flows from the first inlet (Ed) to the first outlet (Sd), the oxygen pressure at the cathode inlet (Ce) being in underpressure with respect to the reference pressure; o characterized in that the electrochemical system is designed to switch between operation in underpressure and what is called operation in overpressure with respect to the reference pressure, and comprises: • a second fluid supply line (Las), connecting a second oxygen inlet (Es) at the reference pressure to the cathode inlet (Ce); • a second fluid discharge line (Les), connecting the cathode outlet (Cs) to a second outlet (Ss); • a pressure regulator, designed to keep the oxygen pressure at the cathode inlet (Ce) constant, and arranged on the second fluid discharge line (Les); • the pump being designed to impose an oxygen flow through the second fluid supply (Las) and discharge (Les) lines, and being arranged on the second fluid supply line (Las); • the second fluid supply (Las) and discharge (Les) lines being designed such that when operating in overpressure, the oxygen flows from the second inlet (Es) to the second outlet (Ss), the oxygen pressure at the cathode inlet (Ce) being kept at overpressure with respect to the reference pressure. o a fuel cell, comprising a cathode inlet (Ce) and a cathode outlet (Cs) which are designed to ensure a flow of oxygen through the fuel cell; o a first fluid supply line (Lad), connecting a first oxygen inlet (Ed) at the reference pressure to the cathode inlet (Ce); o a first fluid discharge line (Led), connecting the cathode outlet (Cs) to a first outlet (Sd); o a pressure reducer, arranged on the first fluid supply line (Lad), and designed to impose a pressure lower than the reference pressure on the oxygen passing through it; o a pump designed to impose an oxygen flow through the first fluid supply (Lad) and discharge (Led) lines, the pump being arranged on the first fluid discharge line (Led), such that when operating in underpressure, the oxygen flows from the first inlet (Ed) to the first outlet (Sd), the oxygen pressure at the cathode inlet (Ce) being in underpressure with respect to the reference pressure; o characterized in that the electrochemical system is designed to switch between operation in underpressure and what is called operation in overpressure with respect to the reference pressure, and comprises: • a second fluid supply line (Las), connecting a second oxygen inlet (Es) at the reference pressure to the cathode inlet (Ce); • a second fluid discharge line (Les), connecting the cathode outlet (Cs) to a second outlet (Ss); • a pressure regulator, designed to keep the oxygen pressure at the cathode inlet (Ce) constant, and arranged on the second fluid discharge line (Les); • the pump being designed to impose an oxygen flow through the second fluid supply (Las) and discharge (Les) lines, and being arranged on the second fluid supply line (Las); • the second fluid supply (Las) and discharge (Les) lines being designed such that when operating in overpressure, the oxygen flows from the second inlet (Es) to the second outlet (Ss), the oxygen pressure at the cathode inlet (Ce) being kept at overpressure with respect to the reference pressure. • a second fluid supply line (Las), connecting a second oxygen inlet (Es) at the reference pressure to the cathode inlet (Ce); • a second fluid discharge line (Les), connecting the cathode outlet (Cs) to a second outlet (Ss); • a pressure regulator, designed to keep the oxygen pressure at the cathode inlet (Ce) constant, and arranged on the second fluid discharge line (Les); • the pump being designed to impose an oxygen flow through the second fluid supply (Las) and discharge (Les) lines, and being arranged on the second fluid supply line (Las); • the second fluid supply (Las) and discharge (Les) lines being designed such that when operating in overpressure, the oxygen flows from the second inlet (Es) to the second outlet (Ss), the oxygen pressure at the cathode inlet (Ce) being kept at overpressure with respect to the reference pressure.