Reivindicaciones
1. A bipolar plate (1) of a proton-exchange membrane fuel cell with an upper face and a lower face characterised in that▪ said plate (1) is made up of titanium, titanium alloys or any of the combinations thereof, ▪ said plate (1) comprises o a first cavity (2) on the upper face and a second cavity (3) on the lower face, a porous material is arranged in said cavities (2, 3), wherein said porous material is made up of titanium, titanium alloys or any of the combinations thereof, wherein the pores of said porous material are interconnected and wherein the pores of said porous material are less than 500 µm in diameter, ∘ at least one first inlet conduit (4) for a first gas or a second gas, wherein said first inlet conduit (4) for a first gas or a second gas is connected to the first cavity (2) through at least one first inlet channel (5) for a first gas or a second gas, ∘ at least one second inlet conduit (10) for a first gas or a second gas, wherein said second inlet conduit (10) for a first gas or a second gas is connected to the second cavity (3) through at least one second inlet channel (11) for a first gas or a second gas, ∘ at least one first outlet conduit (6) for a first gas or a second gas, wherein said first outlet conduit (6) for a first gas or a second gas is connected to the first cavity (2) through at least one first outlet channel (7) for a first gas or a second gas, and ∘ at least one second outlet conduit (8) for a first gas or a second gas, wherein said second outlet conduit (8) for a first gas or a second gas is connected to the second cavity (3) through at least one second outlet channel (9) for a first gas or a second gas, ▪ and said plate (1) is coated with titanium nitride on the entire surface thereof. 2. The bipolar plate (1) according to claim 1, wherein the plate (1) has a thickness between 500 µm and 3 mm. 3. The bipolar plate (1) according to any of claims 1 or 2, wherein the first cavity (2) or the second cavity (3) have an independent thickness between 150 µm and 1 mm. 4. The bipolar plate (1) according to any of claims 1 to 3, wherein the first cavity (2) or the second cavity (3) are arranged concentrically to the bipolar plate (1). 5. The bipolar plate (1) according to any of claims 1 to 4, wherein the first cavity (2) and the second cavity (3) have equal dimensions. 6. The bipolar plate (1) according to any of claims 1 to 5, wherein • the first gas is H<2> and the second gas is O<2> or air, • the first gas is O<2> or air and the second gas is H<2>. 7. The bipolar plate (1) according to any of claims 1 to 6, wherein the porous material arranged in the first cavity (2) and in the second cavity (3) has pores with a size between 500 µm and 250 µm in diameter, of between 150 µm and 250 µm or of less than 150 µm in size. 8. A method for manufacturing the bipolar plate (1) according to any of claims 1 to 7, characterised in that it comprises the following steps: a) pouring powders selected from titanium, titanium hydride, titanium alloys or any combination thereof, into a mould comprising • a first cavity (2) and a second cavity (3), • a first inlet channel (5) and a second inlet channel (10), and • a first outlet channel (7) and a second outlet channel (9), and pressing at a pressure between 100 MPa and 600 MPa; and b) sintering and gas nitriding of the pressed product obtained in step (a) to obtain a preform of the bipolar plate (1) comprising a titanium nitride coating on the surface thereof, c) preparing a homogeneous mixture of • a powder selected from titanium, titanium hydride, titanium alloys or any combination thereof, and • an ammonium bicarbonate powder space holder with a particle size between 250 µm and 500 µm, 150 µm and 250 µm or less than 150 µm, in a mixer operating at a speed between 50 rpm and 60 rpm for at least a period of 1 h, wherein the proportion by volume of ammonium bicarbonate in the mixture is between 50 % v/v and 70 % v/v, d) pouring the homogeneous mixture obtained in step (c) into a mould in the shape of the first cavity (2) and the second cavity (3) and pressing at a pressure of between 100 MPa and 600 MPa; e) removing the ammonium bicarbonate space holder from the product pressed in step (d) by heat treatment at a temperature between 40 °C and 120 °C for a period of time between 4 h and 12 h, f) sintering and gas nitriding of the porous material arranged in the mould in the shape of the first cavity (2) and the second cavity (3) obtained in step (e) to form a titanium nitride coating on said porous material, g) assembling the porous material coated with titanium nitride obtained in step (f) with the preform of the bipolar plate (1) comprising a titanium nitride coating on the surface thereof. 9. The method according to claim 8, said method further comprising an additional step (a1), between step (a) and step (b) of machining the compacted powder obtained in step (a) to form the inlet and outlet conduits (4, 6, 8, 10). 10. The method according to claim 8, wherein the mould used in step (a) further comprises mandrels to form the inlet and outlet conduits (4, 6, 8, 10). 11. The method according to any of claims 8 to 10, wherein, in step (b), vacuum sintering is carried out in a furnace at a temperature between 900 °C and 1400 °C and at a pressure between 0.00001 MPa and 0.01 MPa for a period of time between 1 h and 4 h, and the gas nitriding of the sintered product is carried out in a furnace under a nitrogen atmosphere at a temperature of between 850 °C and 1200 °C for a period of time between 1 h and 4 h, wherein the nitrogen pressure is between 0.05 MPa and 0.2 MPa. 12. The method according to any of claims 8 to 10, wherein, in step (b), sintering is carried out in a furnace at a temperature between 900 °C and 1400 °C, in an argon atmosphere, wherein the argon pressure is between 0.05 MPa and 0.2 MPa, for a period of time between 1 h and 4 h, and the gas nitriding of the sintered product is carried out in a furnace under a nitrogen atmosphere at a temperature of between 850 °C and 1200 °C for a period of time between 1 h and 4 h, wherein the nitrogen pressure is between 0.05 MPa and 0.2 MPa. 13. The method according to any of claims 8 to 10, wherein the sintering and gas nitriding of step (b) is carried out in a single furnace, at a temperature of between 850 °C and 1200 °C first under an argon atmosphere, for a period of time between 30 min and 4 h, wherein the argon pressure is between 0.05 MPa and 0.2 MPa, and then under a nitrogen atmosphere for a period of time between 1 h and 4 h, wherein the nitrogen pressure is between 0.05 MPa and 0.2 MPa. 14. The method according to any of claims 8 to 13, wherein, in step (f), vacuum sintering is carried out in a furnace at a temperature between 900 °C and 1400 °C and at a pressure between 0.00001 MPa and 0.01 MPa for a period of time between 1 h and 4 h, and the gas nitriding of the sintered product is carried out in a furnace under a nitrogen atmosphere at a temperature of between 850 °C and 1200 °C for a period of time between 1 h and 4 h, wherein the nitrogen pressure is between 0.05 MPa and 0.2 MPa. 15. The method according to any of claims 8 to 13, wherein, in step (f), sintering is carried out in a furnace at a temperature between 900 °C and 1400 °C, in an argon atmosphere, wherein the argon pressure is between 0.05 MPa and 0.2 MPa, for a period of time between 1 h and 4 h, and the gas nitriding of the sintered product is carried out in a furnace under a nitrogen atmosphere at a temperature of between 850 °C and 1200 °C for a period of time between 1 h and 4 h, wherein the nitrogen pressure is between 0.05 MPa and 0.2 MPa. 16. The method according to any of claims 8 to 13, wherein the sintering and gas nitriding of step (f) is carried out in a single furnace, at a temperature of between 900 °C and 1200 °C first under an argon atmosphere, for a period of time between 30 min and 4 h, wherein the argon pressure is between 0.05 MPa and 0.2 MPa, and then under a nitrogen atmosphere for a period of time between 1 h and 4 h, wherein the nitrogen pressure is between 0.05 MPa and 0.2 MPa. 17. The method according to any of claims 8 to 16, wherein, in step (b), the titanium nitride coating of the preform of the bipolar plate (1) has a thickness between 0.5 µm and 10 µm. 18. The method according to any of claims 8 to 17, wherein, in step (f), the titanium nitride coating of the porous material has a thickness between 0.5 µm and 10 µm. 19. The method according to any of claims 8 to 18, wherein the titanium nitride coating of the preform of the bipolar plate (1) obtained in step (b) and the titanium nitride coating of the porous material obtained in step (f) have the same thickness. 20. A method for manufacturing the bipolar plate (1) according to any of claims 1 to 7, characterised in that it comprises the following steps: i) pouring powders selected from titanium, titanium hydride, titanium alloys or any combination thereof, into a mould comprising • a first cavity (2) and a second cavity (3), • a first inlet channel (5) and a second inlet channel (10), and • a first outlet channel (7) and a second outlet channel (9), and pressing at a pressure between 100 MPa and 600 MPa; ii) preparing a homogeneous mixture of • a powder selected from titanium, titanium hydride, titanium alloys or any combination thereof, and • an ammonium bicarbonate powder space holder with a particle size between 250 µm and 500 µm, 150 µm and 250 µm or less than 150 µm, in a mixer operating at a speed between 50 rpm and 60 rpm for at least a period of 1 h, wherein the proportion by volume of ammonium bicarbonate in the mixture is between 50 % v/v and 70 % v/v, iii) pouring the homogeneous mixture obtained in step (ii) into the first cavity (2) and into the second cavity (3) of the preform of the bipolar plate (1) obtained in step (i) and pressing at a pressure between 100 MPa and 600 MPa; iv) removing the ammonium bicarbonate space holder from the product pressed in step (iii) by heat treatment at a temperature between 40 °C and 120 °C for a period of time between 4 h and 12 h, v) sintering and gas nitriding of the product obtained in step (iv) to form a titanium nitride coating on said product. 21. The method according to claim 20, said method further comprising an additional step (i1), between step (i) and step (ii), of machining the compacted powder obtained in step (i) to form the inlet and outlet conduits (4, 6, 8, 10). 22. The method according to claim 20, wherein the mould used in step (i) further comprises mandrels to form the inlet and outlet conduits (4, 6, 8, 10). 23. The method according to any of claims 20 to 22, wherein step (iii) is carried out sequentially, wherein the homogeneous mixture obtained in step (ii) is first poured into the first cavity (2) of the mould and pressed at a pressure between 100 MPa and 600 MPa and then the homogeneous mixture obtained in step (ii) is poured into the second cavity (3) of the mould and pressed at a pressure between 100 MPa and 600 MPa. 24. The method according to any of claims 20 to 23, wherein, in step (v), vacuum sintering is carried out in a furnace at a temperature between 900 °C and 1400 °C and at a pressure between 0.00001 MPa and 0.01 MPa for a period of time between 1 h and 4 h, and the gas nitriding of the sintered product is carried out in a furnace under a nitrogen atmosphere at a temperature of between 850 °C and 1200 °C for a period of time between 1 h and 4 h, wherein the nitrogen pressure is between 0.05 MPa and 0.2 MPa. 25. The method according to any of claims 20 to 23, wherein, in step (v), sintering is carried out in a furnace at a temperature between 900 °C and 1400 °C, in an argon atmosphere, wherein the argon pressure is between 0.05 MPa and 0.2 MPa, for a period of time between 1 h and 4 h, and the gas nitriding of the sintered product is carried out in a furnace under a nitrogen atmosphere at a temperature of between 850 °C and 1200 °C for a period of time between 1 h and 4 h, wherein the nitrogen pressure is between 0.05 MPa and 0.2 MPa. 26. The method according to any of claims 20 to 23, wherein the sintering and gas nitriding of step (v) is carried out in a single furnace, at a temperature of between 900 °C and 1200 °C first under an argon atmosphere, for a period of time between 30 min and 4 h, wherein the argon pressure is between 0.05 MPa and 0.2 MPa, and then under a nitrogen atmosphere for a period of time between 1 h and 4 h, wherein the nitrogen pressure is between 0.05 MPa and 0.2 MPa. 27. The method according to any of claims 20 to 26, wherein the titanium nitride coating obtained in step (v) has a thickness between 0.5 µm and 10 µm.
