A method of synthesizing methane by 1-step co-electrolysis of H 2 O and CO 2 in the presence of an electrolyte comprising at least one superprotonic conducting acid compound of the general formula (I) (I) M x H y (AO 4 ) z , wherein x is 1, 2, or 3; y is 1, 2, 3, 4 or 5; z is 1 or 2; M is at least one of Li, Na, K, Rb, Cs, Tl, NH 4 ; and A is S, Se, P, As; said method comprising: a) providing a pressurized electrolytic cell comprising an anode and a cathode, wherein said electrolyte is arranged between said anode and said cathode; and wherein hydrogen ions are produced at said anode according to an anode reaction 4H 2 O → 2O 2 + 8H + + 8e - ; and wherein methane is produced at said cathode according to a cathode reaction CO 2 + 8H + + 8e - → CH 4 + 2H 2 O; said method further comprising operating said electrolytic cell by: b) providing an electrical current applied across said electrolytic cell sufficient to induce anodic and cathodic reactions according to said anode and cathode reactions ; c) maintaining said electrolytic cell at an operating water partial pressure from 1 to 30 bar; d) maintaining said electrolytic cell at an operating temperature sufficient to induce superprotonic conduction in said electrolyte of hydrogen ions produced at said anode; e) providing a flow of gaseous H 2 O as superheated steam as an anode reactants flow to said anode at a flow rate sufficient to allow said anodic reaction; f) providing a flow of gaseous CO 2 as a cathode reactants flow to said cathode at a flow rate sufficient to allow said cathodic reaction; g) collecting a cathode products flow from said cathodic reaction; and h) optionally, isolating methane from said cathode products flow. (I) M x H y (AO 4 ) z , wherein x is 1, 2, or 3; y is 1, 2, 3, 4 or 5; z is 1 or 2; M is at least one of Li, Na, K, Rb, Cs, Tl, NH 4 ; and A is S, Se, P, As; x is 1, 2, or 3; y is 1, 2, 3, 4 or 5; z is 1 or 2; M is at least one of Li, Na, K, Rb, Cs, Tl, NH 4 ; and A is S, Se, P, As; a) providing a pressurized electrolytic cell comprising an anode and a cathode, wherein said electrolyte is arranged between said anode and said cathode; and wherein hydrogen ions are produced at said anode according to an anode reaction 4H 2 O → 2O 2 + 8H + + 8e - ; and wherein methane is produced at said cathode according to a cathode reaction CO 2 + 8H + + 8e - → CH 4 + 2H 2 O; b) providing an electrical current applied across said electrolytic cell sufficient to induce anodic and cathodic reactions according to said anode and cathode reactions ; c) maintaining said electrolytic cell at an operating water partial pressure from 1 to 30 bar; d) maintaining said electrolytic cell at an operating temperature sufficient to induce superprotonic conduction in said electrolyte of hydrogen ions produced at said anode; e) providing a flow of gaseous H 2 O as superheated steam as an anode reactants flow to said anode at a flow rate sufficient to allow said anodic reaction; f) providing a flow of gaseous CO 2 as a cathode reactants flow to said cathode at a flow rate sufficient to allow said cathodic reaction; g) collecting a cathode products flow from said cathodic reaction; and h) optionally, isolating methane from said cathode products flow. <EOS>