Performance of nickel electrode for alkaline water electrolysis prepared by high pressure cold spray

To promote Ni electrode performance during water splitting, a novel coating process, High pressure cold spray, is applied to prepare electrodes from blended Ni + Al powder. By controlling Al fraction, electrodes are obtained with varied microstructure. SEM and EDX are implemented to check the micromorphology of electrodes. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) are performed to estimate the effect of Al addition on electrode performance. Resultantly, significant improvement of electrode performance is achieved by increasing the fraction of Al from 10 vol% to 20 vol%. The obtained coatings are found with numerous pores owing to the removal of Al during the activation. By applying electrochemical test, the HER of all samples are dominated by Volmer step, and sample N20A is found with the highest active surface area. Thus, sample N20A exhibits the highest electro-catalytic activity to HER of alkaline water electrolysis.     

A nano-spherical structure Ni3S2/Ni(OH)2 electrocatalyst prepared by one-step fast electrodeposition for efficient and durable water splitting

Developing non-noble metal catalysts with excellent electrocatalytic performance and stability is of great significance to hydrogen production by water electrolysis, but there are still problems of low activity, complex preparation and high cost. Herein, we fabricated a novel Ni₃S₂/Ni(OH)₂ dual-functional electrocatalyst by a one-step fast electrodeposition on nickel foam (NF). While maintaining the electrocatalytic performance of Ni₃S₂, the existence of heterostructure and Ni(OH)₂ co-catalyst function greatly improves the overall water splitting performance of Ni₃S₂/Ni(OH)₂–NF. Hence, It shows a low overpotential of 66 mV at 10 mA cm^?2 for HER and 249 mV at 20 mA cm^?2 for OER. The dual-functional electrocatalyst needs only 1.58 V at 20 mA cm^?2 when assembled two-electrode electrolytic cell. Impressively, the electrocatalyst also shows outstanding catalytic stability for about 800 h when 20 and 50 mA cm^?2 constant current was applied, respectively which demonstrates a potential electrocatalyst for overall water splitting.     

H2 production by thermochemical water splitting with reticulated porous structures of ceria-based mixed oxide materials

In this work, we present for the first time the preparation and evaluation of Ceria-based mixed oxides reticulated porous ceramic (RPC) structures for H₂ production by thermochemical water splitting. After appropriate screening of the powder materials, ceria-based materials modified with Co, Mn and Zr were discarded due to their low cyclability and/or hydrogen productivity, derived from segregation of active phases or sintering during the thermal reduction and reoxidation. Sponge replica method has been optimized to allow obtaining a Ce_0.9Fe_0.1O_y RPC sponge structure with an outstanding hydrogen production of 15 STPcm³/g_material·cycle at a maximum temperature of 1300 °C. This better performance, comparing to the powder, can be attributed to the open macroporosity of the reticulated porous structure which enhances both heat and mass transfer. The H₂ production is maintained along several consecutive cycles without loss of activity, reinforcing the favorable prospects for large-scale hydrogen production.     

In-Situ solid-state synthesis of 2D/2D interface between Ni/NiO hexagonal nanosheets supported on g-C3N4 for enhanced photo-electrochemical water splitting

Herein, we report a synthesis of 2D/2D interfaces between nickel/nickel oxide (Ni/NiO) hexagonal nanosheets with graphitic-carbon nitride (g-C₃N₄) using an in-situ solid-state heat treatment that shows enhanced activity for electrochemical as well as photo-electrochemical (PEC) water splitting. The transmission electron microscopy characterization confirms the homogenous dispersion of 2D hexagonal nanosheets of Ni/NiO on the surface of g-C₃N₄. The higher electrochemical and PEC water splitting activity of 2D/2D interface may be due to the more intimate contact between 2D sheets of NiO with g-C₃N₄. Moreover, the effect of NiO loading in nanoheterostructures have been studied towards overall water splitting by varying the ratio of precursors for NiO to that of g-C₃N₄ viz. 1:1, 1:8, and 1:16. A compositional ratio of 1:8 have been found to show the best PEC activity towards OER depicting a maximum photocurrent density of 20 mA cm⁻² at an over potential of 190 mV. Whereas, the highest ratio of NiO to g-C₃N₄ nanosheets (i.e. 1:1) was noted to demonstrate the best performance towards electrochemical hydrogen evolution reaction showing dramatically reduced over potential of 26 mV to drive a current density of 10 mA cm⁻².     

Development of durable and efficient electrodes for large-scale alkaline water electrolysis

A new type of electrodes for alkaline water electrolysis is produced by physical vapour depositing (PVD) of aluminium onto a nickel substrate. The PVD Al/Ni is heat-treated to facilitate alloy formation followed by a selective aluminium alkaline leaching. The obtained porous Ni surface is uniform and characterized by a unique interlayer adhesion, which is critical for industrial application. IR-compensated polarisation curves prepared in a half-cell setup with 1 M KOH electrolyte at room temperature reveals that at least 400 mV less potential is needed to decompose water into hydrogen and oxygen with the developed porous PVD Al/Ni electrodes as compared to solid nickel electrodes. High-resolution scanning electron microscope (HR-SEM) micrographs reveal Ni-electrode surfaces characterized by a large surface area with pores down to a few nanometre sizes. Durability tests were carried out in a commercially produced bipolar electrolyser stack. The developed electrodes showed stable behaviour under intermittent operation for over 9000 h indicating no serious deactivation in the density of active sites.     

Controllable fabrication of 3D porous carbon nitride with ultra-thin nanosheets templated by ionic liquid for highly efficient water splitting

Modifying the texture of carbon nitride to adjust its physicochemical performance is a fascinating method for achieving high photocatalytic activity. Herein, we synthesized 3D porous carbon nitride with ultra-thin nanosheets by using cyanuric acid-melamine supramolecular and ionic liquid as precursor and template, respectively. The ionic liquid adjusts the morphology of materials and induces the carbon residue into the porous channels owing to its incomplete degradation. The 3D porous framework makes carbon nitride reflect the enhanced surface area, exposes adequate reaction sites, and offers a pathway for charge transport. And carbon residue and ultra-thin nanosheets further promote the photogenerated carriers transport and reduce the recombination rate of charge carriers. Consequently, 3D porous carbon nitride with ultra-thin nanosheets exhibit outstanding and stable hydrogen evolution under visible light irradiation. Significantly, as-fabricated sample CN-100 reflects an improved H₂ generation rate, up to 17,028 μmol h^?1 g^?1, which is 12 times higher than that of CN (1412 μmol h^?1 g^?1). The present work offers a unique synthesis strategy to develop the novel photocatalyst with efficient photocatalytic performance.     

Electrodeposition of NiS/Ni2P nanoparticles embedded in amorphous Ni(OH)2 nanosheets as an efficient and durable dual-functional electrocatalyst for overall water splitting

To develop earth-abundant and cost-effective catalysts for overall water splitting is still a major challenge. Herein, a unique “raisins-on-bread” Ni–S–P electrocatalyst with NiS and Ni₂P nanoparticles embedded in amorphous Ni(OH)₂ nanosheets is fabricated on Ni foam by a facile and controllable electrodeposition approach. It only requires an overpotential of 120 mV for HER and 219 mV for OER to reach the current density of 10 mA cm⁻² in 1 M KOH solution. Employed as the anode and cathode, it demonstrates extraordinary electrocatalytic overall water splitting activity (cell voltage of only 1.58 V @ 10 mA cm⁻²) and ultra-stability (160 h @ 10 mA cm⁻² or 120 h @50 mA cm⁻²) in alkaline media. The synergetic electronic interactions, enhanced mass and charge transfers at the heterointerfaces facilitate HER and OER processes. Combined with a silicon PV cell, this Ni–S–P bifunctional catalyst also exhibits highly efficient solar-driven water splitting with a solar-to-hydrogen conversion efficiency of 12.5%.     

Electronic regulation and core-shell hybrids engineering of palm-leaf-like NiFe/Co(PO3)2 bifunctional electrocatalyst for efficient overall water splitting

Constructing efficient and stable bifunctional electrocatalysts for overall water splitting remains a challenge because of the sluggish reaction kinetics. Herein, the core-shell hybrids composed of Co(PO₃)₂ nanorod core and NiFe alloy shell in situ grown on nickel foam (NiFe/Co(PO₃)₂@NF) are synthesized. Owing to the hierarchical palm-leaf-like structures and strong adhesion between NiFe alloys, Co(PO₃)₂ and substrates, the catalyst provides a large surface area and rapid charge transfer, which facilitates active sites exposure and conductivity enhancement. The interfacial effect in the NiFe/Co(PO₃)₂ core-shell structure modulates the electronic structure of the active sites around the boundary, thereby boosting the intrinsic activity. Benefiting from the stable structure, the durability of the catalyst is not impaired by the inevitable surface reconfiguration. The NiFe/Co(PO₃)₂@NF electrode presents a low cell voltage of 1.63 V to achieve 10 mA cm^?2 and manifests durability for up to 36 h at different current densities.     

Bi-functional LaMxFe1-xO3 (M = Cu,Co, Ni) for photo-fenton degradation of methylene blue and photoelectrochemical water splitting

Due to growing concern over environmental remediation and the energy crisis, perovskite nanoparticles have gained wide interest in converting solar energy to sustainable fuel and also in degrading organic effluents. Herein, we report the synthesis and bi-functional activity of one-pot-glycine combustion derived LaM_xFe_1-xO₃ (M = Cu, Co, Ni; x = 0, 0.01) for photo-Fenton degradation of Methylene Blue (MB) and photoelectrochemical water splitting. When used as a photocatalyst, with partial substitution of Cu even at a lower concentration, LaCu_0.01Fe_0.99O₃ has exhibited excellent degradation efficiency of 96.4% in 90 min, which is 2.5 times better than the LaFeO₃. On the other hand, Co and Ni modified LaFeO₃ photocatalysts have demonstrated prominent activities with degradation efficiency of 93.8% and 74.8% respectively within 180 min of visible light irradiation. The retention and reusability analysis showed that LaCu_0.01Fe_0.99O₃ is stable against photo corrosion and remains unchanged after 5 consecutive cycles of MB dye degradation. In addition, LaCu_0.01Fe_0.99O₃ is complimented as a single catalyst for dual functions such as photocatalysis and electrocatalysis, both of which are assisted by visible light. Under illumination, the overpotential (η) improved from 507.6 mV vs RHE (dark) to 498.1 mV vs RHE (light) for O₂ evolution and 220.5 mV vs RHE (dark) to 182.8 mV vs RHE (light) for H₂ generation respectively. The light response of the catalyst and improvement in activity is validated by the significant enhancement in current density under exposure at both half cycle of chronoamperometry.