Three-dimensional porous CoNiO2@reduced graphene oxide nanosheet arrays/nickel foam as a highly efficient bifunctional electrocatalyst for overall water splitting

Abstract

It is crucial to develop high-performance and cost-effective bifunctional electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) toward overall water splitting. Herein, a unique heterostructure of reduced graphene oxide (rGO) and CoNiO 2 nanosheets directly grown on nickel foam (NF) were successfully fabricated and applied as a kind of highly efficient bifunctional electrocatalyst. The optimum CoNiO 2 @rGO/NF electrode exhibits excellent electrocatalytic OER performance with an overpotential of only 272 mV to drive a current density of 100 mA•cm −2 , and HER performance with an overpotential of 126 mV to achieve a current density of 10 mA•cm −2. Meanwhile, the electrodes also display outstanding long-term stability for OER and HER with negligible activity and morphology degradation after at least 40 h testing. Furthermore, when employed as both cathode and anode for overall water splitting, CoNiO 2 @rGO/NF electrode only requires 1.56 V at 10 mA•cm −2 and operates stably for over 40 h, which is among the best performing Co-based and Ni-based non-precious metal electrocatalysts. Detailed characterizations reveal that the extraordinary electrocatalytic performance should be attributed to the synergistic effect of the unique heterostructure of CoNiO 2 nanosheets and rGO for increasing the electrode conductivity and integrity, ultrasmall primary particle size for providing larger electrode/electrolyte contact area and abundant active sites, and three-dimensional (3D) conductive networks for facilitating the electrochemical reaction.

The Spin Modulation Stimulated Efficient Electrocatalytic Oxygen Evolution Reaction over LaCoO3 Perovskite

“…The high resolution XPS spectra of Co 2p (Figure 3c and Figure S9) show two main peaks, which are attributed to the Co 2p 3/2 and Co 2p 1/2 levels. The four deconvoluted peaks located at 779.9/794.9 eV and 782.5/797.0 eV are ascribed to the Co 2+ and Co 3+ , respectively, which matches well with the fitting peaks and reported literature, indicating cobalt ions coexist in mixed valence states [41,42] . Significantly, a gradual increase of Co 2+ /Co 3+ can be observed when the post thermal reduction time is prolonged, which may be attributed to the spin state transition and charge compensation.…”

“…The four deconvoluted peaks located at 779.9/ 794.9 eV and 782.5/797.0 eV are ascribed to the Co 2 + and Co 3 + , respectively, which matches well with the fitting peaks and reported literature, indicating cobalt ions coexist in mixed valence states. [41,42] Significantly, a gradual increase of Co 2 + / Co 3 + can be observed when the post thermal reduction time is prolonged, which may be attributed to the spin state transition and charge compensation. The O 1s spectra illustrated in Figure 3d and Figure S10 can be deconvoluted into three peaks, which are assigned to the lattice oxygen atoms (O L ), defective oxygen (O v ) and surface adsorbed oxygen (O c ), respectively.…”

Highly Efficient Oxygen Evolution Reaction Enabled by Phosphorus Doping of the Fe Electronic Structure in Iron–Nickel Selenide Nanosheets

“…[ 8 ] Recently, transition metal‐based (ranging from metal oxides, phosphides, chalcogenides, to emerging single‐atom) catalysts have been considered as promising candidates to replace noble metal‐based catalysts for OER due to their low cost, excellent activity, and high stability. [ 9–12 ] In particular, considerable efforts have been devoted to developing nickel‐iron‐based OER electrocatalysts. [ 7,13,14 ] Among them, NiFe‐selenides have been widely investigated as ideal OER candidates due to the high electronic conductivity, diversity of stable crystal phases, and adjustable electronic structure.…”

Vanadium-Doping and Interface Engineering for Synergistically Enhanced Electrochemical Overall Water Splitting and Urea Electrolysis

“…By optimizing the adsorption/desorption of intermediate species, enhancing conductivity, or increasing active sites, transition metal-based catalysts, such as carbides, , nitrides, , (oxy)­hydroxides, − phosphides (phosphates), − sulfides, , selenides, , and so on, have attracted extensive attention for water electrolysis under alkaline conditions in the past few years. Among the abovementioned candidates, transition metal nitrides, especially Ni 3 N, showing metallic character and corrosion resistance, have been exploited as electrocatalysts toward HER and OER. , However, Ni 3 N has a poor adsorption toward water molecules, and therefore, the electrocatalytic water dissociation rate on it is rather slow .…”