A light-driven fuel cell includes a cathode, an anode, and a proton-permeable membrane between the anode and the cathode. The anode includes a photocatalyst for anaerobic methane oxidation reaction, and when the anode is supplied with methane and water and is irradiated with light, methanol, protons and electrons are generated by anaerobic methane oxidation reaction from the methane and the water supplied to the anode; the protons pass through the proton-permeable membrane and move to the cathode; and the electrons move to the cathode via an external circuit. The cathode includes a photocatalyst for aerobic methane oxidation reaction, and when the cathode is supplied with methane and oxygen and is irradiated with light, methanol and water are generated by aerobic methane oxidation reaction from the methane and the oxygen supplied to the cathode and the protons and the electrons moved from the anode.

A light-driven fuel cell includes a cathode, an anode, and a proton-permeable membrane between the anode and the cathode. The anode includes a photocatalyst for anaerobic methane oxidation reaction, and when the anode is supplied with methane and water and is irradiated with light, methanol, protons and electrons are generated by anaerobic methane oxidation reaction from the methane and the water supplied to the anode; the protons pass through the proton-permeable membrane and move to the cathode; and the electrons move to the cathode via an external circuit. The cathode includes a photocatalyst for aerobic methane oxidation reaction, and when the cathode is supplied with methane and oxygen and is irradiated with light, methanol and water are generated by aerobic methane oxidation reaction from the methane and the oxygen supplied to the cathode and the protons and the electrons moved from the anode.

A device for producing an azo compound includes a reaction unit in which a first solution comprising a hydrazo compound and at least one type of M.sub.aX.sub.b; a negative electrode disposed to be in direct contact with the hydrazo compound inside the reaction unit; and a positive electrode disposed inside the reaction unit so as to be in contact with the solution. X is a halogen element, M is at least one selected from the group consisting of hydrogen, Li, Na, K, Mg, Ca, Mn, Fe, Ni, Cu, Ag, Zn, Sn, Zr, and Ti, or at least one selected from the group consisting of a primary ammonium ion, a secondary ammonium ion, and a tertiary ammonium ion, H is hydrogen, and a and b are each independently any one integer between 1 and 4.

A device for producing an azo compound includes a reaction unit in which a first solution comprising a hydrazo compound and at least one type of M.sub.aX.sub.b; a negative electrode disposed to be in direct contact with the hydrazo compound inside the reaction unit; and a positive electrode disposed inside the reaction unit so as to be in contact with the solution. X is a halogen element, M is at least one selected from the group consisting of hydrogen, Li, Na, K, Mg, Ca, Mn, Fe, Ni, Cu, Ag, Zn, Sn, Zr, and Ti, or at least one selected from the group consisting of a primary ammonium ion, a secondary ammonium ion, and a tertiary ammonium ion, H is hydrogen, and a and b are each independently any one integer between 1 and 4.

A photoexcitable material includes: a solid solution of MN (where M is at least one of gallium, aluminum and indium) and ZnO, wherein the photoexcitable material includes 30 to 70 mol % ZnO and has a band gap energy of 2.20 eV or less.

Methods of selectively modifying lignin, polycarboxylated products thereof, and methods of deriving aromatic compounds therefrom. The methods comprise electrochemically oxidizing lignin using stable nitroxyl radicals to selectively oxidize primary hydroxyls on β-O-4 phenylpropanoid units to corresponding carboxylic acids while leaving the secondary hydroxyls unchanged. The oxidation results in polycarboxylated lignin in the form of a polymeric β-hydroxy acid. The polymeric β-hydroxy acid has a high loading of carboxylic acid and can be isolated in acid form, deprotonated, and/or converted to a salt. The β-hydroxy acid, anion, or salt can also be subjected to acidolysis to generate various aromatic monomers or oligomers. The initial oxidation of lignin to the polycarboxylated form renders the lignin more susceptible to acidolysis and thereby enhances the yield of aromatic monomers and oligomers obtained through acidolysis.

There are provided methods and systems for an electrochemical cell including an anode and a cathode where the anode is contacted with a metal ion that converts the metal ion from a lower oxidation state to a higher oxidation state. The metal ion in the higher oxidation state is reacted with an unsaturated hydrocarbon and/or a saturated hydrocarbon to form products. Separation and/or purification of the products as well as of the metal ions in the lower oxidation state and the higher oxidation state, is provided herein.

The present disclosure relates generally to electrocatalytic process for conversion of a hydrocarbon reactant, comprising: introducing the hydrocarbon reactant into an acidic solution in a presence of a catalyst, wherein the catalyst includes a d° transition metal-oxo moiety; and applying an electrical input to the catalyst to convert the hydrocarbon reactant into a product. The present disclosure also relates to a catalyst for conversion of a hydrocarbon reactant, comprising a d° transition metal-oxo moiety and a sulfonic moiety bonded to the d° transition metal.

The present disclosure relates generally to electrocatalytic process for conversion of a hydrocarbon reactant, comprising: introducing the hydrocarbon reactant into an acidic solution in a presence of a catalyst, wherein the catalyst includes a d° transition metal-oxo moiety; and applying an electrical input to the catalyst to convert the hydrocarbon reactant into a product. The present disclosure also relates to a catalyst for conversion of a hydrocarbon reactant, comprising a d° transition metal-oxo moiety and a sulfonic moiety bonded to the d° transition metal.

A method of forming a hydrocarbon product and hydrogen gas comprises introducing CH.sub.4 to a positive electrode of an electrochemical cell comprising the positive electrode, a negative electrode, and a proton-conducting membrane between the positive electrode and the negative electrode. The proton-conducting membrane comprises an electrolyte material having an ionic conductivity greater than or equal to about 10.sup.−2 S/cm at one or more temperatures within a range of from about 150° C. to about 600° C. A potential difference is applied between the positive electrode and the negative electrode of the electrochemical cell to produce the hydrocarbon product and the hydrogen gas. A CH.sub.4 activation system and an electrochemical cell are also described.