Research Of Sufilde/Three Dimensional Graphene Composites For Artificial Photosynthetic Water Splitting

Energy plays a crucial role in the development of our modern society,and meeting mankind's thirst for sustainable energy systems is one of grand scientific challenges of our time.Artificial photosynthesis devices for water splitting are expected to play a major role in the development of sustainable technologies that alleviate the energy and eviromental challenges.However,the widespread applicaiton of such devices is hampered by the expense of electrocatalysts in the photovoltaic and water splitting apparatus.Recent progress has demonstrated that the low-cost nanostructured metal chalcogenides are very proming candidates for energy conversion and storage systems based on their unique physical and chemical properties.Herein,we successfully synthesized novel morphologies of metal chalcogenides,and hybrid them with three-dimensional?3D?nitrogen doped graphene foam?NGF?.The resulting hybrid materials were further employed in energy conversion and storage devices of artificial photosynthesis apparatus.Moreover,through in situ transmission electron microscopies?TEM?,we clearly captured the real-time information at atomic level of metal chalcogenides in oxygen evolution reaction?OER?process,and unravelled the underlying OER mechanism of the electrocatalysts.The following results are mainly achieved:Firstly,we synthesized well-aligned two-dimensional NixSy nanowalls?2D NixSy NW?on a three-dimensional nitrogen-doped graphene foam?3D NGF?,and further employed it in unassisted APS.Due to the positive synergistic effect between the highly electrocatalytic activity of NixSy NW and excellent conductivity of NGF,this low-cost material of?2D/3D?Ni_xS_y NW/NGF is highly efficient as a multifunctional catalyst in various applications:a counter electrode?CE?for dye-sensitized solar cell?DSSC?,and a“bifunctional”electrocatalyst for oxygen and hydrogen evolution for electrocatalytic overall water-splitting.Furthermore,we connected three Ni_xS_y NW/NGF-based DSSCs as a tandem cell for unassisted solar-driven overall water splitting,using NixSy NW/NGF itself on nickel foams as the anode and cathode.Impressively,such integrated photovoltaic-electrolyser APS device can achieve a solar-to-hydrogen efficiency of 3.2%with an excellent stability and low cost.This work opens an avenue to advanced multifunctional materials for the low-cost and unassisted solar-driven overall water splitting.Secondly,by employing in situ transmission electron microscopy?TEM?,the structural evolution of amorphous electrocatalyst CoSx in OER with nano or even?ngstrom scale resolution is captured,visualizing the process of the electrocatalyst activation.From this in situ observation,we validate that CoSx is converted to crystallized CoOOH on the surface irreversibly with a morphology change via Co?OH?₂ intermediate during OER measurement,where CoOOH is confirmed as the real active species.This conclusion is also supported by multiple ex situ technologies.Furthermore,incorporation of CoSx with a nitrogen-doped graphene foam?NGF?drives a more thoroughly structure transformation and consequently highly improved performance,which is among the best cobalt-based electrocatalysts for OER.We believe this in situ in-depth observation of structural evolution in OER measurement can provide new insights into the fundamental understanding of the mechanism for OER catalysts,thus enable more rational design of low-cost and high-efficient electrocatalysts for water splitting.