From Water Oxidation to Reduction: Homologous Ni–Co Based Nanowires as Complementary Water Splitting Electrocatalysts

Abstract

A homologous Ni–Co based nanowire system, consisting of both nickel cobalt oxide and nickel cobalt sulfide nanowires, is developed for efficient, complementary water splitting. The spinel‐type nickel cobalt oxide (NiCo2O4) nanowires are hydrothermally synthesized and can serve as an excellent oxygen evolution reaction catalyst. Subsequent sulfurization of the NiCo2O4 nanowires leads to the formation of pyrite‐type nickel cobalt sulfide (Ni0.33Co0.67S2) nanowires. Due to the 1D nanowire morphology and enhanced charge transport capability, the Ni0.33Co0.67S2 nanowires function as an efficient, stable, and robust nonnoble metal electrocatalyst for hydrogen evolution reaction (HER), substantially exceeding CoS2 or NiS2 nanostructures synthesized under similar methods. The Ni0.33Co0.67S2 nanowires exhibit low onset potential of −65, −39, and −50 mV versus reversible hydrogen electrode, Tafel slopes of 44, 68, and 118 mV dec−1 at acidic, neutral, and basic conditions, respectively, and excellent stability, comparable to the best reported non‐noble metal‐based HER catalysts. Furthermore, the homologous Ni0.33Co0.67S2 nanowires and NiCo2O4 nanowires are assembled into an all‐nanowire based water splitting electrolyzer with a current density of 5 mA cm−2 at a voltage as 1.65 V, thus suggesting a unique homologous, earth abundant material system for water splitting.

Engineering Pyrite-Type Bimetallic Ni-Doped CoS2 Nanoneedle Arrays over a Wide Compositional Range for Enhanced Oxygen and Hydrogen Electrocatalysis with Flexible Property

“…The binding peak at 168.8 eV is ascribed to the shakeup satellite peak [53]. These XPS results together demonstrate the presence of Ni 2+ /Ni 3+ , Co 2+ /Co 3+ and S 2− /S2 2− in the synthesized NixCo1−xS2 nanostructures, well agree with those reported previously [50]. X-ray photoelectron spectroscopy (XPS) was further performed, to characterize the elemental compositions and surface chemical valences of synthesized Ni-doped CoS 2 in the near-surface range.…”

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

“…Figure 5a shows the overall water splitting activity of two-electrode system with the TiO 2 @Co 9 S 8 electrocatalysts as both cathode and anode in 1 m KOH solution (denoted as TiO 2 @Co 9 S 8 || TiO 2 @Co 9 S 8 ). Impressively, a significantly low cell voltage of 1.56 V is obtained at the current density of 10 mA cm −2 (Figure 5a), substantially lower than the Co 9 S 8 || Co 9 S 8 catalyzer cell (1.71 V) and other reported bifunctional electrocatalysts, [6,16,27,[38][39][40][41][42][43][44][45][46] (Figure 5b), and even close to the Pt/C || IrO 2 (1.54 V) catalyzer cell. [44] Figure 5c compares the chronopotentiometry curves of the TiO 2 @Co 9 S 8 || TiO 2 @Co 9 S 8 and Co 9 S 8 || Co 9 S 8 catalyzer cells collected at 10 mA cm −2 .…”

“…[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.…”

Acid promoted Ni/NiO monolithic electrode for overall water splitting in alkaline medium

“…S12b). The resulting Tafel slope of NF-120 is 46 mV dec −1 , smaller than that of the other catalysts (51,52,53 and 63 mV dec −1 for NF-90, NF-60, NF-20 min and NF-10 min). This is a sign of more favorable kinetics with a more rapid oxygen evolution rate.…”

“…S8d) reveal an obviously decreased charge transfer resistance after the acid-activation, which means more rapid charge transfer kinetics. The improved charge transfer ability could promote the combination of electrons and Hads, and benefit the electrical integration to minimize concomitant Ohmic losses [52,53], and thus the electrocatalytic activity was enhanced. The good HER performance of Ni/NiO can be attributed to the low hydrogen adsorption impedance and fast charge-transfer kinetics on the surface of the electrode.…”