3D porous and self-supporting Ni foam@graphene@Ni3S2 as a bifunctional electrocatalyst for overall water splitting in alkaline solution

NiFe LDH/Fe2O3/Ni3S2 Heterostructure with a Superhydrophilic/Superaerophobic Surface for Solar-Driven Electrolytic Water Splitting

The development of a bifunctional electrocatalyst with high efficiency, high stability, and low cost is of great significance in practical applications of electrocatalytic water splitting. Herein, a self-supporting bifunctional electrocatalyst with a NiFe layered double hydroxide/Fe2O3/Ni3S2 heterostructure (NiFe LDH/Fe2O3/Ni3S2/IF) for hydrogen evolution and oxygen evolution reactions (HER/OER) is synthesized by the self-corrosion of iron foam (IF) and hydrothermal strategies. The constructed NiFe LDH/Fe2O3/Ni3S2/IF hierarchical heterostructure was not only beneficial to expose active sites and promote charge/mass transfer but also generate a superhydrophilic/superaerophobic surface, thereby accelerating the reaction kinetics to improve the HER/OER activity. Therefore, NiFe LDH/Fe2O3/Ni3S2/IF exhibited superior overpotentials of 226.2 and 162.8 mV for the OER and HER at 100 mA cm-2, respectively. NiFe LDH/Fe2O3/Ni3S2/IF was employed as both the cathode and the anode to assemble a device for overall water splitting and displayed a voltage of 1.55 V at 10 mA cm-2. The overall water splitting device was coupled with a solar cell to simulate a solar-powered water splitting system, resulting in a superior solar-to-hydrogen conversion efficiency of 15.16%. This work can promote the development of clean energy sources such as solar hydrogen production.

Electrodeposition of Ni nanoparticles from deep eutectic solvent and aqueous solution promoting high stability electrocatalyst for hydrogen and oxygen evolution reactions

Nanostructured Ni films were synthesized from two distinct baths and were assessed as electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 M KOH. Herein, Ni was electrodeposited from two separate solvents, the aqueous acetate buffer and ethaline solvent as a kind of deep eutectic solvents (DESs), and both the deposited films were investigated as electrocatalysts for HER and OER. The electrodeposition parameters such as pH and deposition potential were studied. The electrodeposition process was performed using chronoamperometry technique and Ni deposits were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Fabricated Ni@PGE deposit from ethaline only requires an overpotential of − 154 mV and 350 mV to achieve a current density of 10 mA cm−2 for HER and OER, respectively. While, Ni@PGE from acetate requires an overpotential of − 164 mV and 400 mV to produce the current density of 10 mA cm−2 for HER and OER.

Graphical abstract

Iron, rhodium-codoped Ni2P nanosheets arrays supported on nickel foam as an efficient bifunctional electrocatalyst for overall water splitting

To enhance the overall water splitting efficiency, it is widely attractive yet challenging to develop low price, abundance and efficient bifunctional electrocatalysts towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, Fe,Rh-codoped Ni₂P nanosheets arrays were in situ anchored on three-dimension (3D) Ni foam under hydrothermal condition and successive phosphorization, denoted as Fe,Rh-Ni₂P/NF for simplicity. The unique nanosheets arrays effectively enriched the active sites with easy accessibility. By virtue of the unique sheet-like arrays and 3D porous conductive substrate, the prepared Fe,Rh-Ni₂P/NF showed the low overpotentials of 226 mV at 30 mA cm^-2 towards the OER and 73 mV at 10 mA cm^-2 for the HER. Moreover, the electrocatalyst effectively worked as anode and cathode for overall water splitting system, showing a small voltage of 1.62 V to drive a current density of 10 mA cm^-2. The present work provides alternative option for fabricating advanced catalysts in electrocatalysis and energy devices.

Three-Dimensional Graphene-Based Macrostructures for Electrocatalysis

Electrochemical energy storage and conversion is an effective strategy to relieve the increasing energy and environment crisis. The sluggish reaction kinetics in the related devices is one of the major obstacles for them to realize practical applications. More efforts should be devoted to searching for high-efficiency electrocatalysts and enhancing the electrocatalytic performance. 3D graphene macrostructures (3D GMs) are one kind of porous crystalline materials with 3D structures at both micro- and macro-scale. The unique structure can achieve large accessible surface area, expose many active sites, promote fast mass/electron transport, and provide wide room for further functional modification. All these features make them promising candidates for electrocatalysis. In this review, the authors focus on the latest progress of 3D GMs for electrocatalysis. First, the preparation methods of 3D GMs are introduced followed by the strategies for functional modifications. Then, their electrocatalytic performances are discussed in detail including monofunctional and bifunctional electrocatalysis. The electrocatalytic processes involve oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and carbon dioxide reduction reaction. Finally, the challenges and perspectives are presented to offer a guideline for the exploration of excellent 3D GM-based electrocatalysts.