Phase-Controlled NiO Nanoparticles on Reduced Graphene Oxide as Electrocatalysts for Overall Water Splitting

Abstract

Efficient water electrolysis is one of the key issues in realizing a clean and renewable energy society based on hydrogen fuel. However, several obstacles remain to be solved for electrochemical water splitting catalysts, which are the high cost of noble metals and the high overpotential of alternative catalysts. Herein, we suggest Ni-based alternative catalysts that have comparable performances with precious metal-based catalysts and could be applied to both cathode and anode by precise phase control of the pristine catalyst. A facile microwave-assisted procedure was used for NiO nanoparticles anchored on reduced graphene oxide (NiO NPs/rGO) with uniform size distribution in ~1.8 nm. Subsequently, the Ni-NiO dual phase of the NPs (A-NiO NPs/rGO) could be obtained via tailored partial reduction of the NiO NPs/rGO. Moreover, we demonstrate from systematic HADDF-EDS and XPS analyses that metallic Ni could be formed in a local area of the NiO NP after the reductive annealing procedure. Indeed, the synergistic catalytic performance of the Ni-NiO phase of the A-NiO NPs/rGO promoted hydrogen evolution reaction activity with an overpotential as 201 mV at 10 mA cm−2, whereas the NiO NPs/rGO showed 353 mV. Meanwhile, the NiO NPs/rGO exhibited the most excellent oxygen evolution reaction performance among all of the Ni-based catalysts, with an overpotential of 369 mV at 10 mA cm−2, indicating that they could be selectively utilized in the overall water splitting. Furthermore, both catalysts retained their activities over 12 h with constant voltage and 1000 cycles under cyclic redox reaction, proving their high durability. Finally, the full cell capability for the overall water electrolysis system was confirmed by observing the generation of hydrogen and oxygen on the surface of the cathode and anode.

Versatile Janus Architecture for Electrocatalytic Applications

“…[64] The presence of TM and TMO components in a catalyst often facilitates bifunctional electrocatalysis, whereby the metal and metal oxide components possess catalytic activity for different reactions. [65,66] Commonly, TM/TMO materials are formed through annealing at high temperatures, to convert part of the TM to TMO. [65,66] However, the distribution of metallic and oxide components in the resultant material may be difficult to control, thus making it difficult to guarantee the formation of separate functional domains which do not interfere with one another.…”

Morphology-Controlled Nickel Oxide and Iron–Nickel Oxide for Electrochemical Oxygen Evolution Reaction

“…In general, a Randles circuit consists of three components: solution resistance (R s ), double-layer capacitance (C dl ), and charge transfer resistance (R ct ). 38 Since the R s value is constant under the same experimental conditions, a low R ct value indicates fast charge-transfer kinetics on the catalyst surface. In Figure 6e,f, the hexagonal and donut-shaped Fe-doped samples exhibit the lowest R ct values of 33.5 and 36.5 Ω, respectively; the other iron−nickel oxide samples exhibit a moderate charge-transfer rate.…”

“…In addition, EIS measurements were performed to determine the charge transfer rate kinetics for the various samples. In general, a Randles circuit consists of three components: solution resistance ( R s ), double-layer capacitance ( C dl ), and charge transfer resistance ( R ct ) . Since the R s value is constant under the same experimental conditions, a low R ct value indicates fast charge-transfer kinetics on the catalyst surface.…”

MOF-Derived Porous Fe3O4/RuO2-C Composite for Efficient Alkaline Overall Water Splitting

“…This requires extra energy to break the O–H bond and finally form the O–O bond. Thus, it has been considered as the rate-limiting step in overall water splitting. , This multielectron transfer process with high energy barriers slows the kinetics of hydrogen (H 2 ) and oxygen (O 2 ) production, thus limiting its application in industries. − Generally, commercial platinum on carbon (Pt/C) and ruthenium oxide (RuO 2 ) is considered as the state-of-the-art catalyst for HER and OER, respectively. , However, their high price and low durability are of great concern for further industrial applications. , Although there are several lower transition metal-based catalysts for overall water splitting in base media, their results are still not satisfying for practical application. − There are several strategies to improve the catalytic activity, such as formation of oxide, , hydroxide, nitride, sulfide, phosphide, selenide, etc. Among them, synthesis of oxide-based materials with the presence of interfaces is getting importance nowadays.…”