Structural Engineering And Water Splitting On Heterostructured Nickel/Cobalt Chalcogenide Electrocatalysts

To address the rapid growth of energy consumption and the associated environment issues,renewable and clean energy sources?e.g.,H₂?have attracted immense research interest on the global levels.Hydrogen is one of the sustainable energy sources attracting much attention,which can be produced via water electrolysis.Nickel,cobalt and other metal chalcogenides are new type of non-noble metal electrocatalysts,which are featured by excellent conductivity,high catalytic activity,low price,and bi-functionality for both hydrogen and oxygen evolution.They are promising as the substitutes of high-cost noble-metal materials.This work proposes the construction of metal sulfide and selenide heterostructures to fulfill interfacial synergy and optimiz the intrinsic activity for electrocatalysis.Meanwhile,hierarchical nanowires evenly integrating 1D and 2D building blocks are designed to promote the exposure of highly active herterointerfaces.As a result,high efficiencies in HER,OER,and overall water splitting are successfully achieved.1.One-pot synthesis was introduced for MoS₂-Ni₃S₂ heteronanorods supported by Ni foam?MoS₂-Ni₃S₂ HNRs/NF?,in which the Ni₃S₂ nanorods were hierarchically integrated with MoS₂ nanosheets.The hierarchical MoS₂-Ni₃S₂ heteronanorods allow not only the good exposure of highly active heterointerfaces but also the facilitated charge transport along Ni₃S₂ nanorods anchored on conducting nickel foam,accomplishing the promoted kinetics and activity for HER,OER,and overall water splitting.The optimal MoS₂-Ni₃S₂ HNRs/NF presents low overpotentials(?₁₀)of 98and 249 mV to reach a current density of 10 mA cm^-2 in 1.0 M KOH for HER and OER,respectively.Assembled as an electrolyzer for overall water splitting,such heteronanorods show a quite low cell voltage of 1.50 V at 10 mA cm^-2 and remarkable stability for more than 48 hours,which are among the best values of current noble-metal-free electrocatalysts.2.Alkaline water electrolysis has been receiving special attentions because of the benefit for O₂ evolution at relatively low overpotential.However,the sluggish HER kinetics in a basic environment,associated with the difficult generation of initial hydrogen intermediate(denoted as H_ads)from discharging H₂O(H₂O+e^-?H_ads+OH^-),causes high overpotential and associated large energy consumption in water electrolysis on noble-metals or Pt-free electrocatalysts.Herein,we designed hierarchical and free-standing electrocatalysts on conducting nickel foam?NF?,which comprised of one-dimensional?1D?CoNiSe₂ surface-decorated with two-dimensional?2D?Co-Ni layered-double-hydroxide?denoted as CoNiSe₂@CoNi-LDHs/NF?.They afforded rich heterointerfaces to efficiently catalyze HER and OER,featuring by the low overpotentials(?₁₀)of 110 and 210 mV to reach a current density?j?of 10 mA cm^-2 in 1.0 M KOH,respectively.The obviously promoted HER was identified on selenide-LDHs interfaces,which accelerated water dissociation to produce H_ads on neighboring CoNiSe₂ sites;while negligible effects were observed in OER.Moreover,structural alterations on heterointerfaces confirmed by in-situ Raman analysis were responsible for the deterioration in electrocatalysis,highlighting the importance of such heterointerfaces.The composites further revealed a superior activity for overall water splitting with a quite low cell voltage of 1.43 V at 10 mA cm^-2,outperforming most of current noble-metal-free materials,and even a benchmarking IrO₂/C-Pt/C couple.3.The?Ni/Co?₃S₄/NF electrocatalyst can be prepared from the facile sulfidation of 1D Co-Ni precursors.The as-obtained catalysts afforded high activity in HER and OER,featuring the low?₁₀ of 122 and 205 mV,respectively.In summary,we proposed feasible strategies to construct and optimize the heterostructures of nickel/cobalt chalcogenides toward efficient HER,OER,and overall water splitting.The relevant structure-activity relationship was studied in detail.This work will open up new opportunities to develop efficient electrocatalysts via rational engineering on interfaces and nanostructures.