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Surface treatment is an effective method to improve the photoelectrochemical (PEC) performance of photoelectrodes. Herein, we introduced a novel strategy of surface sulfurization to modify hematite (α-Fe2O3) nanorods grown in an aqueous solution, which triggered encouraging improvement in PEC performances. In comparison to the solution-grown pristine α-Fe2O3 nanorod photoanode that is PEC inefficient and always needs high temperature (>600 °C) activation, the surface sulfurized α-Fe2O3 nanorods show photocurrent density increased by orders of magnitude, reaching 0.46 mA cm−2 at 1.23 V vs. RHE (reversible hydrogen electrode) under simulated solar illumination. This improvement in PEC performances should be attributed to the synergy of the increased carrier density, the reduced surface charge carrier recombination and the accelerated water oxidation kinetics at the α-Fe2O3/electrolyte interface, as induced by the incorporation of S ions and the formation of multi-state S species (Fe-Sx-Oy) at the surface of α-Fe2O3 nanorods. This study paves a new and facile approach to activate α-Fe2O3 and even other metal oxides as photoelectrodes for improved PEC water splitting performances, by engineering the surface structure to relieve the bottlenecks of charge transfer dynamics and redox reaction kinetics at the electrode/electrolyte interface.

Bismuth vanadate (BiVO4) is one of the most promising metal oxide semiconductors for photoelectrochemical (PEC) water oxidation. Much efforts have been dedicated on accelerating the sluggish surface water oxidation kinetics. In this study, plasma enhanced atomic layer deposition and subsequent removal of Al2O3 ultrathin overlayers on bismuth vanadate were implemented to achieve the successful passivation of surface states and significant enhancement of PEC performance. Al2O3 ultrathin overlayers were first coated on BiVO4 surface via plasma enhanced atomic layer deposition with various deposition cycles, which resulted in the decrease of PEC water oxidation activity due to the poor conductivity. The subsequent removal of surface amorphous Al2O3 passivated the surface states of the photoanodes and significantly enhanced the photocurrent densities. The passivated BiVO4 exhibited a photocurrent density of 1.34 mA·cm−2 at 1.23 V vs. RHE, which is 73% higher than that of unmodified BiVO4. This work provides a novel strategy and deep insights on surface modification of semiconductor for photoelectrochemical energy conversion.

In this study, we report a simple, effective and universal approach to fabricate homojunction structural TiO2 nanorod array photoelectrodes through doping of gradient distributed oxygen vacancies introduced by annealing in high vacuum with controlled time. The homogeneous junction structure promotes the separation and transport of photoexcited charge carriers, and the photocurrent density of TiO2 nanorod arrays annealed in high vacuum for 2 h was 20 times higher than that of the pristine TiO2 nanorod arrays. The results indicate that annealing in high vacuum with controlled time could form a homojunction structure, which is an effective approach for further enhancing the performance of UV–visible light driven photocatalytic materials for water splitting.

Given the proper band gap, low cost and good stability, hematite (α-Fe2O3) has been considered as a promising candidate for photoelectrochemical (PEC) water splitting, however suffers from the sluggish surface water oxidation reaction kinetics. In this study, a simple dip-coating process was used to modify the surface of α-Fe2O3 nanorod arrays with cobalt oxide (CoOx) and carbon (C) for the improved PEC performance, with a photocurrent density at 1.6 V (vs. reversible hydrogen electrode, RHE) increased from 0.10 mA/cm2 for the pristine α-Fe2O3 to 0.37 mA/cm2 for the CoOx/C modified α-Fe2O3 nanorods. As revealed by electrochemical analysis, thanks to the synergistic effect of CoOx and C, the PEC enhancement could be attributed to the enhanced charge transfer ability, decreased surface charge recombination, and accelerated water oxidation reaction kinetics. This study serves as a good example for improving PEC water splitting performance via a simple method.

Novel hybrid tetra-nitro-phthalocyanine Copper(II) (TNCuPc)/TiO2 films were successfully synthesized using a simple hydrothermal and solvothermal method. The successful deposition of TNCuPc on the TiO2 nanorods was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The precursor concentration for hydrothermal deposition of TiO2 was optimized for light absorption and photoelectrochemical (PEC) water splitting. The hierarchical nanostructure exhibited increased light absorption ability and enhanced PEC properties. Moreover, the concentration of the precursor solution for TNCuPc deposition was also optimized for the performance of the TNCuPc/TiO2 hybrid nanostructure. The optimal sample achieved the highest photocurrent of 1.1 mA cm−2 and the highest IPCE of 51% at 610 nm.

In this study, a ternary nanostructured α-Fe2O3/Au/TiO2 film with integrating a crystalline α-Fe2O3 core, metallic Au nanoparticles (NPs), and an amorphous TiO2 overlayer is fabricated and examined as a photoanode for photoelectrocatalytic water splitting. Under simulated solar illumination, the as-prepared photoanode exhibits a four-fold increase (1.05 mA cm−2) in photocurrent density at 1.23 V versus reversible hydrogen electrode (RHE) relative to bare α-Fe2O3. Based on systematic investigations, it is proposed that Au NPs extract photoholes from the bulk of α-Fe2O3 core and then shuttle them to the outer TiO2 overlayer, and meanwhile, TiO2 overlayer efficiently captures and stores the photoholes and facilitates the hole injection into electrolyte. Thus, the remarkably improved photoelectrocatalytic water splitting performance of α-Fe2O3/Au/TiO2 photoanode is attributed to the significantly suppressed bulk and surface charge recombination due to the relayed pumping of the photogenerated charge carriers through the photoanode/electrolyte interfaces reconstructed by Au NPs and TiO2 overlayer.

The article by Wang, Lin and Chou illustrates the integration and control of a 500W self-humidified proton exchange membrane fuel cell (PEMC) system. By applying some classic modern control theory as tools, some robust controllers are designed to regulate the air and hydrogen flow rates. In this article, the authors give detailed design procedure from the mathematical modeling to the controller design. Somemodern control theories, such as systems identification, Hinf control and optimal control are synthetically used. In the Hinf control based design, a key problem is the selection of the weighting function. In this article, such a procedure is shown in details. Due to these reason, in our opinion thework of this article can be viewed as a successful practical application of advanced control theory. It may help to reduce the gap between control theory and control engineering. The overall design procedure of the considered 500W self-humidified PEMC system includes the following aspects.