▎ 摘　　要

NOVELTY - Nanocomposite comprises heteroatom-doped graphene and heteroatom-doped carbon nanotubes (CNTs). The nanocomposite has a heteroatom content of at least 1 wt.%. USE - The nanocomposite is useful: in an electrode; in a battery that is a lithium battery; as a catalyst for a reduction reaction, where the reduction reaction is a hydrogen evolution reaction, an oxygen reduction reaction or reduction of carbon dioxide; as a catalyst for an oxidation reaction; as a catalyst for splitting water; in an electrochemical cell for splitting water; in a photoelectrochemical cell; and for reducing carbon dioxide to carbon dioxide-reduction products (all claimed). ADVANTAGE - The nanocomposite: has heteroatom-doped graphene which does not form agglomerates of more than about ten layers (claimed); and provides light weight and flexible photoelectrochemical cells that may be used at a higher temperature and/or a higher pressure in order to tune product selectivity, and have a modular design, enabling easy scale-up and easy disassembly if required. DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: (1) a process (p1) of producing the nanocomposite, comprising (a) providing heteroatom-doped graphene, (b) providing heteroatom-doped CNTs, and (c) combining the heteroatom-doped graphene and heteroatom-doped CNTs in a solution to form the nanocomposite; (2) use of the nanocomposite as a catalyst for a reduction reaction; (3) use of the nanocomposite as a catalyst for an oxidation reaction, or as a catalyst for splitting water; (4) a photoelectrochemical cell comprising: an anode comprising at least one oxidation catalyst; a cathode comprising at least one reduction catalyst, where the cathode is in electrical communication with the anode; and a proton conductor having a porous structure, where the proton conductor connects the anode and the cathode, thus allowing transfer of protons between the anode and the cathode; (5) the proton conductor which allows permeation of a gas through the proton conductor; (6) a process (p2) for preparing a porous proton conductor, comprising providing a proton-conducting polymeric material, and electrospinning the polymeric material, thus producing a porous proton conductor; and (7) reducing carbon dioxide to carbon dioxide-reduction products, comprising: providing water vapor and carbon dioxide gas stream to the photoelectrochemical cell, where the water vapor contacts the oxidation catalyst and the carbon dioxide gas contacts the reduction catalyst; exposing the anode to an electromagnetic radiation source, thus converting the water vapor to oxygen gas, protons and/or electrons; transporting the protons and electrons to the cathode via the proton conductor; and exposing the cathode to the electromagnetic radiation source, thus reducing the carbon dioxide gas in the presence of the protons and electrons to carbon dioxide reduction products.