1D@2D Hierarchical Structures of Co(OH)_x Nanosheets on NiMoO_x Nanorods Can Mediate Alkaline Hydrogen Evolution with Industry‐Level Current Density and Stability

Abstract

Pt, RuO 2 , IrO 2 , etc.) are the most efficient hydrogen evolution reaction (HER) electrocatalysts, but their high cost and low abundance limit their industrial applications. [9][10][11][12] Therefore, it is significant to prepare non-precious metal electrocatalysts with low cost and high performance.Transition metal-based materials, such as alloys, sulfides, hydroxides, nitrides, oxides, and so on, have been widely used as HER electrocatalysts in alkaline water electrolysis. Among them, nickelmolybdenum alloy-based materials are considered to be the most promising and cheapest substitutes for noble metal catalysts in alkaline environments because nickel sites are good water dissociation centers and molybdenum sites feature excellent hydrogen adsorption properties. [13][14][15][16] However, the molybdenum in the nickel-molybdenum alloy is very easy to precipitate, which significantly limits the further application of the nickelmolybdenum alloy under the high current density. [17] Recently, researchers found that the larger negative binding energy of transition metal hydroxides can facilitate the HER process by reducing the adsorption energy of H 2 O and the Gibbs free energy of adsorbed H*. [18][19][20] In particular, cobalt hydroxides (Co(OH) x ), a highly active Volmer promoter, can promote water splitting through the instantaneous formation of intermediate H* atoms during alkaline HER process. Furthermore, twodimensional (2D) layered Co (OH) x with relatively open structure facilitates the diffusion of products and accelerates proton-coupled electron transfer. [21][22][23] To generate Co(OH) x promoters for alkaline HER, the metallic cobalt (Co 0 ) precatalyst components usually undergo rearrangement of the surface structure under the action of electrons to form hydroxide/oxyhydroxide species during the electrochemical process. [24] Thus, metallic Co 0 can be deposited on the surface of the electrocatalyst in advance, and then the in situ grown Co(OH) x catalyst can be obtained by electrochemical activation process. To meet practical industrial applications, the precatalyst can be constructed on 3D porous substrates such as nickel foam (NF) to avoid the agglomeration of active materials and ensure a certain mechanical strength, which provides a certain prerequisite for the stable use of electrocatalysts at high current densities. [25][26][27][28] Herein, we report an electrocatalyst synthesis strategy, where the alkaline HER performance was greatly enhanced by constructing a

Rational Design of Hydrogen Evolution Reaction Electrocatalysts for Commercial Alkaline Water Electrolysis

“…[ 154,155 ] Recently, our group designed a multidimensionally hierarchical structure with 1D Co(OH) x NSs growing on 2D NiMoO x nanorods. [ 151 ] The nanorods enhance the electrochemically active surface area of the electrode, while the 2D Co(OH) x NSs attached to NiMoO x nanorods accelerate the mass transfer effect from the electrode to the electrolyte due to the heterogeneous interface between the two components. Surprisingly, Co(OH) x @NiMoO x @NF remained stable at 1000 mA cm −2 for 11 days with no visible decay ( η 1000 = 332 mV).…”

“…Co-P [140] 1 M KOH / 290 1000 mA cm À2 for 3000 h Ni─Co─P/CFP [136] 1 M KOH 170 295 1000 mA cm À2 for 300 h CoMoS X /NF [87] 1 M KOH 269 / 500 mA cm À2 for 100 h PS-Cu [146] 1 M KOH / 1200 (1200 mA cm À2 ) 100 mA cm À2 for 30 h CuMo 6 S 8 /Cu [147] 1 M KOH / 320 (1000 mA cm À2 ) 2500 mA cm À2 for 100 h 334 (2500 mA cm À2 ) Design of electrode surface Co(OH) x @NiMoO x @NF [151] 1 M KOH 185 322 1000 mA cm À2 for 11 days Ni 2 P-CoOOH [150] 1 M KOH %160 %400 (2000 mA cm À2 ) %1800 mA cm À2 for 100 h MoS 2 /Mo 2 C [50] 1 M KOH 191 220 200 mA cm À2 for 20 h…”

“…Modifying the macrostructure of the catalyst on the electrode, for instance, the structure of the multidimensional catalytic surface can effectively expose more active sites per unit mass to improve HER performance. [44,[150][151][152][153] Moreover, the multidimensional structure implies a closer interface between the electrode and the electrolyte, which shortens the ion diffusion path and facilitates the release of bubbles. [154,155] Recently, our group designed a multidimensionally hierarchical structure with 1D Co(OH) x NSs growing on 2D NiMoO x nanorods.…”

Synergistic Tuning of CoO/CoP Heterojunction Nanowire Arrays as Efficient Bifunctional Catalysts for Alkaline Overall Water Splitting

“…What's more, the specific surface area of the catalyst can be improved by the uniform growth on the support, as well as enhanced stability by inhibiting active site agglomeration through anchoring effects, and improved electronic conductivity by promoting the charge transfer between the catalyst and the support. [23][24][25][26][27] Despite significant progress in the study of transition metal-based self-supported catalysts, little progress has been made in the study of heterojunction self-supported catalysts composed of transition metal oxides and phosphides.…”

Amorphous Oxysulfide Reconstructed from Spinel NiCo2S4 for Efficient Water Oxidation

“…[1,2] One of the key technologies for hydrogen production from renewable energy is electrochemical water splitting. [3][4][5][6] However, the anodic oxygen evolution reaction (OER) process with sluggish kinetics and high energy barriers have Wang's group [35] used cationic defect engineering to preferentially generate a large number of Co defects on spinel NiCo 2 O 4 . Theoretical calculations and experiments demonstrate that Al doping elongates the CoO bonds and promotes the ionization of Co under plasma treatment.…”