Design And Construction Of Aligned And Porous Monolithic Carbon Film Electrodes For High-current-density Hydrogen Generation

Energy shortage and environmental pollution are currently the two major challenges faced by human beings,rendering the development of advanced clean energy technologies with vital significance for our national mission of carbon neutrality.Hydrogen is the most promising clean energy due to its high energy density,high thermal conversion efficiency and zero-carbon emission.Hydrogen can be produced from the hydrogen evolution reaction（HER）via the electrochemical water splitting process,which is considered to be a clean,highly efficient and sustainable method,and its large-scale employment relies on the development of high-performance and cost-effective electrocatalysts.Recently,single atom catalysts（SACs）and metal cluster catalysts（MCCs）have aroused wide attention in the field of electrocatalysis for their high atom utilizatio n efficiency and excellent intrinsic activity.Although a variety of noble metal-based and non-precious-metal-based SACs and MCCs have been developed for catalyzing the HER,most of them can only operate at low current densities,making them unsuitable to be used at high current densities demanded by practical applications.To this end,designing monolithic electrodes is highly critical for industrial applications,which can solve the major problems faced by conventional powdery and slurry-based electrodes under high current densities,such as insufficient number of active sites,inhibited mass transport and poor stability.Herein,based on the advantages of monolithic electrodes in mass transport,catalyst loading and other aspects,three-dimensional porous carbon films with vertically aligned channels are employed as substrates for loading metal single atoms and nanoclusters with high intrinsic activity by high-temperature pyrolysis and electrochemical deposition.The as-prepared monolithic electrodes can efficiently and stably produce hydrogen under high current densities.The main contents are listed as follows:（1）Aligned porous carbon film electrode decorated with cobalt single atoms（Co–NC–AF）has been developed by high-temperature pyrolysis.Co–NC–AF as an HER electrode is able to deliver high current densities up to 1000 m A cm^–2at anηas low as 343 m V and continuously produce hydrogen at 1000 m A cm^-2 for at least 32 h under static condition in 0.5 M H₂SO₄.Combined analyses of XAFS,TEM,surface wettability and electrochemical measurements suggest that the excellent HER performance of Co–NC–AF at high current densities could be attributed to:（a）Co single atom sites possess high intrinsic activity including low onsetηand small charge transfer resistance;（b）The monolithic carbon film electrodes with high catalyst loading can provide abundant active sites;（c）T he vertically aligned structure,multiscale porosity,along with the desirable surface wettability of superhydrophilicity and under-water superaerophobicity,are beneficial in improving the transport efficiency of electrons,ions and gases,enabling Co–NC–AF to operate efficiently and stably under high current densities.This work demonstrates the application of SACs toward hydrogen production at high current densities for the first time and promotes the practical application of SACs.（2）A monolithic carbon film electrode co-modified with Pt single atoms and Pt clusters（Pt SA/NC–AF）with ultralow loading has been prepared by electrochemical deposition using the aligned porous carbon film as substrates.Benefiting from the interaction of Pt single atoms and Pt nanoclusters,Pt SA/NC–AF exhibits excellent HER performance under high current densities in acidic electrolyte,with anηof 139 m V at a current density of 1000 m A cm^-2.Despite the ultralow Pt loading（0.038 wt%）in the catalyst,Pt SA/NC–AF displays an ultrahigh mass activity(888.6 A mg _Pt^-1@100 m V)and high intrinsic activity(TOF=904.9 s^-1@100 m V).This simple,fast and efficient electrochemical deposition method provides a new avenue for the preparation of metal single-atom and cluster catalysts and additionally promotes the application of high-performance and cost-effective noble metal-based catalysts in high-rate hydrogen production under industrially relevant current densities.