Heterointerface and Defect Dual Engineering in a Superhydrophilic Ni₂P/WO_2.83 Microsphere for Boosting Alkaline Hydrogen Evolution Reaction at High Current Density

Abstract

Developing a high-performance electrocatalyst for hydrogen evolution reaction (HER) requires a comprehensive consideration of the three key factors, that is, intrinsic activity, electric conductivity, and active site number. Herein, we report the facile synthesis of a self-supported Ni2P/WO2.83 heterointerface microsphere as a highly active and low-cost catalyst for alkaline HER, which has simultaneously addressed these key issues by a joint application of heterointerface construction and defect and architecture engineering strategies. Our density functional theory calculations revealed Ni2P and WO2.83 optimized by the interface coupling effect work in concert to improve the intrinsic activity of the catalyst. Importantly, the metalloid Ni2P in an intimate combination with the oxygen-defect-rich WO2.83 species endowed the electrocatalyst with high conductivity. Furthermore, the Ni2P/WO2.83 electrocatalyst presented a superhydrophilic nanostructure, ensuring abundant active sites and their accessibility. Benefiting from these attributes, the obtained Ni2P/WO2.83 heterointerface electrocatalyst exhibited excellent activity along with favorable stability for alkaline HER, especially at high current density, surpassing the most reported non-precious catalysts.

Interfacial Coupling and Defect-Induced Dual Effects Enabling Superhydrophilic Ni2P/V2O3–x Heteronanosheets to Accelerate Alkaline Hydrogen Evolution Reaction

“…According to the Tafel plot fitted from the polarization curves (Figure b), the targeted catalyst showed a small Tafel slope with a value of 78 mV·dec –1 , which was similar to that of Pt/C (56 mV·dec –1 ) and lower than those of Ni 2 P/NF (106 mV·dec –1 ), V 2 O 3 /NF (112 mV·dec –1 ), Ni 3 V 2 O 8 /NF (116 mV·dec –1 ), and bare NF (159 mV·dec –1 ). Such fitted results suggested that the HER pathway over the series of catalysts should follow the Volmer–Heyrovsky mechanism with the Volmer step (H 2 O dissociation) as the rate-controlling step, and the smaller Tafel slope of Ni 2 P/V 2 O 3– x /NF catalyst implied an accelerated Volmer step by a rational combination of TMPs and defect-rich metal-oxides, which is in line with previous studies about concerted catalysts …”

“…Such fitted results suggested that the HER pathway over the series of catalysts should follow the Volmer−Heyrovsky mechanism with the Volmer step (H 2 O dissociation) as the rate-controlling step, and the smaller Tafel slope of Ni 2 P/ V 2 O 3−x /NF catalyst implied an accelerated Volmer step by a rational combination of TMPs and defect-rich metal-oxides, which is in line with previous studies about concerted catalysts. 30 The aforementioned apparent HER performance may be overestimated because of the high specific surface area of nanomaterials. In an effort to accurately evaluate the intrinsic HER activity of the target catalyst, we further measured the electrochemical C dl of Ni 2 P/V 2 O 3−x /NF to calculate their ECSA and normalized the obtained current, particularly in comparison with that of V 2 O 3 /NF and Ni 2 P/NF catalysts.…”

“…In an effort to accurately evaluate the intrinsic HER activity of the target catalyst, we further measured the electrochemical C dl of Ni 2 P/V 2 O 3−x /NF to calculate their ECSA and normalized the obtained current, particularly in comparison with that of V 2 O 3 /NF and Ni 2 P/NF catalysts. Among them, the value of the C dl was calculated by cyclic voltammetry (CV) measurements (Figure S5) performed at various scan rates (10,20,30,40, and 50 mV•s −1 ). Figure 4c showed that the Ni 2 P/V 2 O 3−x /NF catalyst possessed a much larger C dl value (89.5 mF•cm −2 ) than those of Ni 2 P/NF (42.6 mF•cm −2 ) and V 2 O 3 /NF (5.76 mF•cm −2 ) samples.…”

“…25 Generally, the metal-(hydr)oxides are effective for cleaving the HO-H bond, whereas many transition metals and their alloys/ compounds are efficient for facilitating the H* associative desorption. 26,27 In practice, several TMPs-based heterostructure electrocatalysts, like Ni 2 P/MoO 2 , 28 CoP/CeO 2 , 29 Ni 2 P/ WO 2.83 , 30 and MoP/MoO 2 , 31 have been successfully developed for accelerating the alkaline HER. Nevertheless, thusconstructed TMP/metal-(hydr)oxides heterostructure catalysts may sacrifice charge transfer kinetics and thereby lower its HER activity, as metal-(hydr)oxides typically possess poor electrical conductivity.…”

“…The benefit behind is that it may potentially provide new functionality for boosting the reactions involved multiple rate-limiting steps (like alkaline HER), as which is typically constructed by different types of materials with diverse properties. , For the alkaline HER, it was typically accepted that the involved reaction pathways are consist of H 2 O dissociation (Volmer step) and hydrogen intermediates (H*) associative desorption (Heyrovsky or Tafel step) . Generally, the metal-(hydr)­oxides are effective for cleaving the HO-H bond, whereas many transition metals and their alloys/compounds are efficient for facilitating the H* associative desorption. , In practice, several TMPs-based heterostructure electrocatalysts, like Ni 2 P/MoO 2 , CoP/CeO 2 , Ni 2 P/WO 2.83 , and MoP/MoO 2 , have been successfully developed for accelerating the alkaline HER. Nevertheless, thus-constructed TMP/metal-(hydr)­oxides heterostructure catalysts may sacrifice charge transfer kinetics and thereby lower its HER activity, as metal-(hydr)­oxides typically possess poor electrical conductivity .…”