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A uniform dendritic NiCo 2 S 4 @NiCo 2 S 4 hierarchical nanostructure of width ≈100 nm is successfully designed and synthesized. From kinetic analysis of the electrochemical reactions, those electrodes function in rechargeable alkaline batteries (RABs). The dendritic structure exhibited by the electrodes has a high discharge-specific capacity of 4.43 mAh cm −2 at a high current density of 240 mA cm −2 with a good rate capability of 70.1% after increasing the current densities from 40 to 240 mA cm −2 . At low scan rate of 0.5 mV s −1 in cyclic voltammetry test, the semidiffusion controlled electrochemical reaction contributes ≈92% of the total capacity, this value decreases to ≈43% at a high scan rate of 20 mV s −1 . These results enable a detailed analysis of the reaction mechanism for RABs and suggest design concepts for new electrode materials.

We present a highly active copper oxide composite photoelectrode with improved stability and photoelectrochemical performance brought about by a simple cycle of heat treatment and cathodic reduction. Under one sun (AM 1.5 G, 100 mW/cm2) light illumination, the photocurrent density of a Cu2O/CuO/Al2O3 composite electrode was enhanced to −1.8 mA/cm2 at 0 V vs RHE compared to −0.25 mA/cm2 of the native Cu2O film. The improved stability of the film was demonstrated by ∼60% retention of initial photocurrent (−1.1 mA/cm2) after 20 sequential cyclic voltammetry scans. Moreover the photocurrent showed only a slight decrease in activity after five regeneration cycles. Furthermore, a high incident photo-to-current efficiency (IPCE, 53% at 450 nm) was recorded. These enhancements in both photocurrent and stability are due to electron transfer from Cu2O to CuO and increase of carrier density due to the presence of Al2O3.

In the synthesis method of a BiVO4 photoanode via BiOI flakes, a BiOI film is formed by electrochemical deposition in Step 1, and a vanadium (V) source solution is placed by drop-casting on the BiOI film in Step 2. Following this, BiVO4 particles are converted from the BiOI–(V species) precursors by annealing. However, it is challenging to evenly distribute vanadium species among the BiOI flakes. As a result, the conversion reaction to form BiVO4 does not proceed simultaneously and uniformly. To address this limitation, in Step 2, we developed a new electrochemical deposition method that allowed the even distribution of V2O5 among Bi–O–I flakes to enhance the conversion reaction uniformly. Furthermore, when lactic acid was added to the electrodeposition bath solution, BiVO4 crystals with an increased (040) peak intensity of the X-ray diffractometer (XRD) pattern were obtained. The photocurrent of the BiVO4 photoanode was 2.2 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE) under solar simulated light of 100 mW/cm2 illumination. The Faradaic efficiency of oxygen evolution was close to 100%. In addition, overall water splitting was performed using a Ru/SrTiO3:Rh–BiVO4 photocatalyst sheet prepared by the BiVO4 synthesis method. The corresponding hydrogen and oxygen were produced in a 2:1 stoichiometric ratio under visible light irradiation.

A simplistic and low-cost method that dramatically improves the performance of solution-grown hematite photoanodes for solar-driven water splitting through incorporation of nanohybrid metal oxide overlayers was developed. By heating the α-Fe 2 O 3 /SnO 2 –TiO 2 electrode in an inert atmosphere, such as argon or nitrogen, the photocurrent increased to over 2 mA/cm 2 at 1.23 V versus a reversible hydrogen electrode, which is 10 times higher than that of pure hematite under 1 sun (100 mW/cm 2 , AM 1.5G) light illumination. For the first time, we found a significant morphological difference between argon and nitrogen gas heat-treated hematite films and discussed the consequences for photoresponse. The origin for the enhancement, probed via theoretical modeling, stems from the facile incorporation of low formation energy dopants into the Fe 2 O 3 layer at the interface of the metal oxide nanohybrid overlayer, which decreases recombination by increasing the electrical conductivity of Fe 2 O 3 . These dopants diffuse from the overlayer into the α-Fe 2 O 3 layer readily under inert gas heat treatment. This simple yet effective strategy could be applied to other dopants to increase hematite performance for solar energy conversion applications.