Hollow TiO₂@Co₉S₈ Core–Branch Arrays as Bifunctional Electrocatalysts for Efficient Oxygen/Hydrogen Production

Abstract

water splitting is recognized as a highly potential technology to convert electricity into environment friendly and renewable chemical fuels (hydrogen and oxygen). [1][2][3] The cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) depend heavily on the development of cost-effective high-performance electrocatalysts. [4,5] Currently, platinum (Pt)/Pt-based alloy and iridium/ruthenium oxides (IrO 2 /RuO 2 ) are considered as the most promising electrocatalysts for HER and OER, respectively, but their scarcity, high cost, and compromised stability hinder their widespread applications. [6,7] Additionally, the best working situation for those OER and HER catalysts is often mismatchable since OER preferably takes place in alkaline or neutral solution while HER in acidic medium. [8,9] This would cause compromised performance for overall water splitting. For instance, the commercial alkaline electrolyzers require high cell voltages (1.8-2.0 V) to drive water splitting, [10] far ahead of the theoretical value of ≈1.23 V owing to high overpotentials on the sluggish of OER and HER. Therefore, it is highly desirable to explore alternative high-performance and low-cost bifunctional OER/HER electrocatalysts for overall water splitting. [11][12][13][14][15] Over the past decades, great progress has been achieved on the development of non-noble metal-based electrocatalysts for both OER and HER. Various nonprecious metal oxides, [9] sulfides, [16] selenides, [17] phosphides, and nitrides [18,19] have been exploited. Among these electrocatalysts, cobalt sulfide (Co 9 S 8 ) is regarded as an attractive electrocatalyst for water splitting due to its high catalytic activity for HER and OER simultaneously, and excellent electrochemical stability. In comparison to bulk Co 9 S 8 , nanostructured Co 9 S 8 and its composites could afford more active sites and faster transfer rate of ions/electrons during the electrocatalytic reaction, and thus usually exhibiting enhanced HER and OER activities. [20][21][22][23][24] Currently, several Co 9 S 8 nanostructures (e.g., nanoparticles [25] and nanospheres [26] ) and their composites with carbons (Co 9 S 8 /reduced graphene oxides (RGO), [22] Co 9 S 8 /(N, S, P)-doped carbons, [27] Co 9 S 8 /Fe 3 O 4 / RGO, [23] and Co 9 S 8 /MoS 2 /Carbon fibres [25] ) have been reported. For example, Co 9 S 8 /N,P-carbon powder nanocomposites prepared by molten-salt calcination method at 900 °C exhibited an HER overpotential of 261 mV at 10 mA cm −2 in alkaline medium. [20] N-Co 9 S 8 /graphene nanocomposites was achieved Designing ever more efficient and cost-effective bifunctional electrocatalysts for oxygen/hydrogen evolution reactions (OER/HER) is greatly vital and challenging. Here, a new type of binder-free hollow TiO 2 @Co 9 S 8 core-branch arrays is developed as highly active OER and HER electrocatalysts for stable overall water splitting. Hollow core-branch arrays of TiO 2 @Co 9 S 8 are readily realized by the rational combination of crosslinked Co 9 S 8 nanoflakes on ...

Tailoring the d‐Band Centers Enables Co4N Nanosheets To Be Highly Active for Hydrogen Evolution Catalysis

“…Herein, we successfully endowC o 4 Nw ith prominent HER catalytic capability by tailoring the positions of the d-band center through transitionmetal doping.T he V-doped Co 4 Nn anosheets displaya n overpotential of 37 mV at 10 mA cm À2 ,w hich is substantially better than Co 4 Na nd even close to the benchmark Pt/C catalysts.X ANES,U PS,a nd DFT calculations consistently reveal the enhanced performance is attributed to the downshift of the d-band center,w hich helps facilitate the Hd esorption. Herein, we successfully endowC o 4 Nw ith prominent HER catalytic capability by tailoring the positions of the d-band center through transitionmetal doping.T he V-doped Co 4 Nn anosheets displaya n overpotential of 37 mV at 10 mA cm À2 ,w hich is substantially better than Co 4 Na nd even close to the benchmark Pt/C catalysts.X ANES,U PS,a nd DFT calculations consistently reveal the enhanced performance is attributed to the downshift of the d-band center,w hich helps facilitate the Hd esorption.…”

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Endowing materials with specific functions that are not readily available is always of great importance,b ut extremely challenging.C o 4 N, with its beneficial metallic characteristics,h as been proved to be highly active for the oxidation of water,w hile it is notoriously poor for catalyzing the hydrogen evolution reaction (HER), because of its unfavorable d-band energy level. [2b] To this end, exploring earth-abundant and catalytically active non-noble-metal-based catalysts,s uch as transition-metal nitrides, [3] phosphides, [4] sulfides, [5] selenides, [6] and carbides, [7] is highly imperative.Tr ansition-metal nitrides have emerged as an interesting family of HER catalysts,b ecause of their high electrical conductivity and noble-metal-like behavior. This concept could provide valuable insights into the design of other catalysts for HER and beyond.

Hydrogen holds great promise in the development of clean energy systems,because of its high gravimetric energy density and environmental friendliness.

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“…[1] Alkaline electrolysis has been viewed as the most feasible way for the industrial production of hydrogen. [2b] To this end, exploring earth-abundant and catalytically active non-noble-metal-based catalysts,s uch as transition-metal nitrides, [3] phosphides, [4] sulfides, [5] selenides, [6] and carbides, [7] is highly imperative. [2b] To this end, exploring earth-abundant and catalytically active non-noble-metal-based catalysts,s uch as transition-metal nitrides, [3] phosphides, [4] sulfides, [5] selenides, [6] and carbides, [7] is highly imperative.…”

Defect‐Rich Heterogeneous MoS2/NiS2 Nanosheets Electrocatalysts for Efficient Overall Water Splitting

“…[11][12][13][14][15] As for tuning the morphology, constructing 2D TMS nanosheets could generate abundant electroactive sites because of inherent large specific surface and rich active edges. [18][19][20] Further, interface modification could be another effective approach to engineering the physical or chemical properties of electrocatalysts. [18][19][20] Further, interface modification could be another effective approach to engineering the physical or chemical properties of electrocatalysts.…”

A general ligand-assisted self-assembly approach to crystalline mesoporous metal oxides

“…To advance our understanding of the enhancement in OER activity, the electrochemically active surface area (ECSA) of the as-prepared catalysts was tested by electrochemical capacitance surface area measurements [35][36][37][38] . The ECSA is positively proportional to the double-layer capacitance (C dl ) (Fig.…”