Multipronged Fabrication of Co₃Se₄ Wrapped into N‐Doped Multiwall Carbon Nanotubes Tangled Hollow Dodecahedron Framework for Overall Water Splitting under Benign Condition

Abstract

and renewability, is recognized as an ideal alternative, and its byproduct is only water when it is used as a fuel. [3,4] However, over 90% of hydrogen is produced through fossil fuel conversion, a process that consumes nonrenewable resources and releases CO 2 gas, deteriorating the energy crisis and the risk of global warming. [5] Electrolysis of water, by contrast, is an important technique for future hydrogen economy, which can convert electricity into clean energy depositing in molecular hydrogen. [6,7] And the driving electricity can be supplied from the intermittentrenewable resources, for instance solar, wind and tidal energy. [8,9] In the standard state, electrolysis of water only requests a theoretical voltage of 1.23 V to trigger the reaction. [10] But both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are kinetically unfavorable, demanding extra energy input to conquer the reaction energy barrier. [1,11] Consequently, the high-performance electrocatalysts are extremely necessary to reduce the reaction activation energy barriers and ameliorate the energy-transfer efficiency. [4,12] Although Pt-based materials and noble metal oxides (like RuO 2 and IrO 2 ) are recognized as high-performance HER and OER catalysts, their booming cost, poor durability, and onefold functionality seriously hinder the industrial application in the large scale.To solve this issue, the earth-abundant and cost-effective transition metal-based electrocatalysts have been widely studied. [2,13] However, these catalysts usually display an unsatisfied compatibility with two half reactions and poor stability in acidic or alkaline electrolyte, due to the different thermodynamic character for HER and OER. [14,15] Therefore, a high-effective bifunctional catalyst that can simultaneously drive HER and OER needs to be developed for simplifying equipment and reducing operation cost. [16,17] Besides, in traditional water electrolysis system, the use of highly acidic (proton exchange membrane) or alkaline (alkaline water electrolyzer) electrolyte is regular practice in this field. [18] Unfortunately, such overall water splitting is usually restricted by device corrosion and environmental In this work, a synergistic strategy is proposed to synthesize a highperformance bifunctional electrocatalyst (marked as Co 3 Se 4 /N-CNTs) for neutral water splitting, in which Co 3 Se 4 nanoparticles are wrapped into N-doped multiwall carbon nanotubes assembled hollow dodecahedron framework. The neutral-oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalytic performances of Co 3 Se 4 /N-CNTs are maximally optimized by regulating nanostructure engineering, element doping, and carbon coating. In 1 m phosphate buffer solution (PBS) electrolyte, Co 3 Se 4 /N-CNTs catalyst exhibits superior stability and catalytic activity for OER and HER, yielding a geometrical catalytic current density of 10 and −10 mA cm −2 at rather low overpotentials of 385 and 102 mV, respectively, meanwhile operating continuously for 35 h wit...

Effect of Iron and Vanadium Doping on Structural Phase Transition in Cobalt Diselenide Enabling Superior Oxygen/Hydrogen Electrocatalysis

“…FeV-a/m-Co 3 Se 4 has superior ORR activity due to its nonstoichiometric structure 2 and intrinsically catalytic Co 3+ species, which facilitate oxygen adsorption in electrochemical reactions. 25,59 Additionally, the high surface area consisting of numerous hierarchical mesopores could maximize active site exposure and promote mass diffusion.…”

“…Figure f shows that after 20 h of continuous operation, the FeV-a/ m -Co 3 Se 4 catalyst retains 92.7% of its original voltammetry current, whereas the Pt/C catalyst dwindles to 76%. FeV-a/ m -Co 3 Se 4 has superior ORR activity due to its nonstoichiometric structure and intrinsically catalytic Co 3+ species, which facilitate oxygen adsorption in electrochemical reactions. , Additionally, the high surface area consisting of numerous hierarchical mesopores could maximize active site exposure and promote mass diffusion. After the chronoamperometry test, the loaded materials were separated from the electrode and examined using SEM (Figure S8a), HR-TEM (Figure S8b,c), and XPS (Figure S9).…”

“…Along with the demand to substitute endangered elements, the development of innovative non-precious-metal electrocatalysts incorporating multifunctional electrocatalytic operations into one catalyst entity will lead to a dramatic simplification of the manufacturing processes, as well as significantly decrease manufacturing costs. , For OER and HER, transition-metal-based catalysts have been extensively studied owing to their abundance and are considered promising alternatives. ,, There has been considerable interest in cobalt-based bimetal oxides and selenides due to their remarkable OER properties in alkaline media, especially mesoporous nanostructures. − ,− In particular, cobalt selenides offer a unique approach to structural transformation engineering that makes them suitable candidates. Specifically, stoichiometric CoSe 2 , with its t 2g 6 e g 1 structure, ,, is considered to be an appropriate electrode material for oxygen and hydrogen electrocatalysis, ,, and its performance has been experimentally demonstrated.…”

“…Specifically, stoichiometric CoSe 2 , with its t 2g 6 e g 1 structure, ,, is considered to be an appropriate electrode material for oxygen and hydrogen electrocatalysis, ,, and its performance has been experimentally demonstrated. However, bulk CoSe 2 lacks electrocatalytic activity and has poor electronic conductivity. , Consequently, in recent years, morphologies of CoSe 2 have been tuned, , combined with carbon materials, ,, heterostructured, ,, and doped with heteroatoms to enhance their catalytic performance. ,− Despite its promising HER and OER performance, CoSe 2 I still need to be applied, due to its slow kinetics, unpredictable stability, and unsatisfactory activity . Through the control of P-doping, structural transformation engineering has been accomplished, and orthorhombic-CoSe 2 (o-CoSe 2 ) obtained through doping has shown better HER performances than the original cubic-CoSe 2 It is confirmed by Dai’s report that, with the introduction of Cu (II) ions, o-CoSe 2 is transformed into m-Co 3 Se 4 (monoclinic phase-Co 3 Se 4 ).…”

Edge-Rich 3D Structuring of Metal Chalcogenide/Graphene with Vertical Nanosheets for Efficient Photocatalytic Hydrogen Production

“…Hydrogen has been extensively studied as an ideal clean energy source to replace conventional fossil fuels. Photocatalytic and photoelectrochemical (PEC) hydrogen generation by water splitting using sunlight is a promising strategy to produce hydrogen fuel by harvesting solar energy for energy storage use. − Transition metal compounds or Transition metal chalcogenides (TMDs), which are two-dimensional (2D) layered structures, have revitalized an upsurge in research interest because of exceptional electronic, photoelectric, and energy harvesting performance. − Among these TMDs, molybdenum disulfide (MoS 2 ) and tungsten disulfide (WS 2 ) have recently attracted considerable attention as a suitable material for cocatalysis or photocatalytic hydrogen generation due to their relatively high mobility (a few hundred cm 2 V –1 s –1 ), superior catalytic properties, and an adequate bandgap that is compatible with sunlight. − …”