Study On Carbon-based Composite Nanomaterials For Photovoltaics-driven Hydrogen Evolution

Solar power and hydrogen are two important renewable energy sources.Combining photovoltaic conversion and water electrolysis is an effective strategy to achieve hydrogen production driven by renewable energy.However,a challenging issue for an efficient photovoltaic conversion is to achieve both high conductivity and transparency simultaneously for the transparent electrode materials used in solar cells.Conventional transparent electrode materials such as indium tin oxide?ITO?have disadvantages including brittleness,ion migration and very limited indium resources.Moreover,to realize a cost-effective hydrogen production from water electrolysis,transition metal dichalcogenides?TMDCs?have been explored for hydrogen evolution reaction?HER?catalysis to reduce the dependence on traditional noble metals?e.g.Pt?.However,there are some challenges that limit the practical applications of TMDCs as efficient HER catalysts,such as the poor catalytic activity of their basal planes,large resistance of electron transport and insufficient exposure of active edge sites.Carbon-based nanomaterials have excellent physical and chemical properties such as high conductivity,high specific surface and good stability,which are expected to be new alternative electrode materials and synergistic component for applications in photovoltaics and water electrolysis.In this dissertation,controllable growth of graphene and carbon nanotube?CNT?films is achieved by atmospheric pressure chemical vapor deposition,and the photovoltaic conversion performance of carbon-based electrodes in solar cells is optimized.By using a two-step method of electrospinning and subsequent sulfurization treatment,the structures of TMDC/carbon composite catalysts?WS₂/C and MoS₂/C?are well controlled,thus their electrocatalytic performances are optimized.The solar cells are connected in series with the water electrolysis cell to construct a carbon-based photovoltaic-driven hydrogen production system.The main findings are:?1?By using large-area,high-quality graphene and CNT films as both anode and cathode electrodes,a semitransparent,flexible organic solar cell with all-carbon electrodes is assembled.The interfacial properties and charge transportation and collection in the carbon-based electrodes are studied and discussed.The open circuit voltage of the solar cell can reach0.62 V,which is much better than that of the ITO counterpart device?0.48 V?.?2?By adjusting the synthesis parameters and post-purification treatment,the photoelectric properties of the graphene and CNT films are optimized.Their light transmission and sheet resistance are further improved.Carbon/silicon hybrid solar cells are fabricated with graphene and CNT films,demonstrating a power conversion efficiency of 7.0%,comparable to that of the reported solar cells with noble metal grid top electrodes.?3?By using plasma pretreatment and adding pore-forming agent in precursor,the morphology of WS₂/C and MoS₂/C can be controlled,which makes the WS₂ or MoS₂ nanoplates vertically embedded in the carbon fibers that have high-specific surface.In these carbon-based composite materials,abundant active edges,high active site densities and high-speed electron transport paths have obtained,which lead to excellent catalytic performance in acid electrolyte.The high current density of 675 mA/cm² at overpotential of 400 mV is achieved,which is close to the target of industrial hydrogen production by water electrolysis.Through theoretical calculations and kinetic analysis,the growth mechanism and catalytic mechanism of the composite structure are proposed.The carbon-based hybrid solar cell is connected to a hydrogen evolution electrolytic cell,and WS₂/C and MoS₂/C are used as free-standing catalytic electrodes to integrate a carbon-based non-precious metal photovoltaic-driven hydrogen evolution system,through which the solar-to-hydrogen conversion efficiency of 4.4⁴.6%is achieved.