Optimization of Photoelectrochemical Response on TiO2 Nanotube Arrays Treated by H3PO4 and Mechanism Analysis of the Slowing Down Effect during Preparation.

The process control of anodization has been a hot topic for a long time. In this study, the addition of phosphoric acid to the traditional electrolyte changed the ion distribution on the reaction interface and the composition of the anion contamination layer so as to achieve the slowing down effect on anodization, the mechanism and theoretical model of which are also given in this paper. TiO2 is a common material in photoelectrocatalysis, but there are few studies on the photoelectrochemical performance of TiO2 nanotube arrays. The stability and rapidity of the photoelectrochemical response of TiO2 nanotube arrays prepared in phosphoric acid containing an electrolyte were effectively optimized in this study.

Heterogeneous Fe-Doped NiCoP-MoO3 Efficient Electrocatalysts for Overall Water Splitting.

Transition metal phosphides with excellent performance are one of the effective alternatives to noble metal catalysts in overall water splitting. In this paper, the Fe-NiCoP-MoO3 composite was prepared by a facile synthesis as the bifunctional electrocatalyst. Fe-NiCoP-MoO3 achieves an operating current density of 10 mA/cm2 at a low overpotential of 65 mV for hydrogen evolution reaction and drives an operating current density of 50 mA/cm2 at only 293 mV for oxygen evolution reaction. Significantly, Fe-NiCoP-MoO3 was employed as the anode and cathode for overall water splitting, which only requires a cell voltage of 1.586 V to reach 10 mA/cm2 as well as shows excellent stability. The electrocatalytic activity of Fe-NiCoP-MoO3 exceeds most of the recently reported typical bifunctional electrocatalysts. This may be due to the coupling effect between the polymetallic phosphides. In addition, heterogeneous catalysts generally expose more active sites than homogeneous catalysts. In addition, replacing MoO3 with WO3 and VO3 can also improve the performance of Fe-NiCoP. This work provides an idea for the modification of phosphides.

Preparation of low-cost perovskite solar cells with high-quality perovskite films in an ambient atmosphere.

High-quality perovskite films are extremely crucial to obtain perovskite solar cells with excellent photovoltaic performance, especially for carbon-based hole transport materials (HTM)-free perovskite solar cells. In this work, a facile and low-cost double two-step method (DT-method) is developed to prepare uniform and pinhole-free CH3NH3PbI3perovskite films in an ambient atmosphere by utilizing the dissolution-recrystallization of PbI2in DMF. That is to spin-coat PbI2and CH3NH3I solution sequentially onto pristine perovskite films prepared by the conventional two-step method. The solar cells fabricated by the DT-method show a dramatic performance improvement, includingVoc,Jsc, and fill factor reach 0.85 V, 15.56 mA cm-2, and 0.58 respectively, which increase power conversion efficiency from 3.93% to 7.58% compared with the conventional two-step method. The improvement in performance and stability of solar cells is mainly due to the higher coverage of perovskite films onto the underlying mesoporous TiO2layer and a negligible amount of PbI2residue, which can effectively reduce charge recombination and promote the rapid transfer of charge carriers. In summary, this work presents a process for preparing carbon-based HTM-free perovskite solar cells (PSCs) in a high-humidity atmospheric environment (60%-85%). This simple device structure and preparation condition can greatly reduce the production threshold and cost of PSCs.

In-situ construction defect-rich CuNiCoS4 /1T-MoS2 heterostructures as superior electrocatalysts for water splitting.

Rational design and construction of bifunctional heterostructure electrocatalysts with high-conductivity and more active sites is imperative for water splitting. Herein, based on the tunable property of layered double hydroxide laminates cations, topological transformation technology and template confine method, a series of high-performance bifunctional catalysts composed of transition metal doping NiCo2S4 (MNiCoS4, M = Cu, Fe, Zn, Mn) and 1T-MoS2 were in-situ fabricated on nickel foam. In particular, CuNiCoS4/1T-MoS2 exhibits an ultralow overpotential of 163 mV at 50 mA cm-2 for oxygen evolution reaction (OER) and favorable hydrogen evolution reaction activity. The two-electrode system requires only 1.52 V to attain a current density of 10 mA cm-2. To the best of our knowledge, its OER electrocatalytic activity far exceed state-of-art catalysts reported. The outstanding performance of this series of catalysts can be attributed to two aspects. First, the highly conductive 1T-MoS2 can facilitate electron transfer, and second, the defect-rich heterostructure can effectively regulate the electronic structure of the active metal and expose abundant active sites. This work provides a valuable strategy for developing high activity electrocatalysts for efficient water splitting.

Anchoring Ni3S2/Cr(OH)3 hybrid nanospheres on Ti3C2@NF dual substrates by ion exchange for efficient urea electrolysis.

Developing efficient nonprecious-metal urea oxidation reaction (UOR) electrocatalysts will promote large-scale hydrogen production via electrolytic water splitting. Therefore, on dual substrates consisting of nickel foam (NF) with high-conductivity Ti3C2 adsorbed on it, Ni3S2/Cr(OH)3 nanosphere catalysts were facilely in situ constructed at room temperature via an ion-exchange method. The optimized electrode exhibits obvious advantages and excellent stability in a solution of 1 M KOH containing 0.5 M urea, with an overpotential of 130 mV at 10 mA cm-2 for the UOR. The two-electrode system requires merely 1.52 V to attain a current density of 10 mA cm-2, and shows excellent durability over 60 h. The superior performance of the electrode is mainly attributed to the following three aspects: (i) the introduction of amorphous Cr(OH)3, which improves the catalyst morphology and regulates the electronic structure of the active metal; (ii) the synergistic catalysis by the defect-rich Ni3S2 and Cr(OH)3 on the nanospheres; (iii) the large adsorption surface and excellent electrical conductivity provided by the dual substrates; and (iv) the mild preparation process, which provides excellent stability for the electrode. The ingenious structural design and simple preparation method of Ni3S2/Cr(OH)3-Ti3C2@NF provide ideas for the development of low-cost, high-efficiency UOR electrodes with industrial application prospects.

Ultrathin NiCo-LDH regulated by CuNiCo trimetallic spinel sulfides as highly active and stable electrocatalysts for overall water splitting.

The rational design of heterostructures, including the synthesis of candidate materials and the construction of structures, is particularly important for the activities of electrocatalysts. Herein, a unique heterostructure of ultrathin NiCo-LDH wrapped CuNiCo trimetallic spinel sulfides was constructed via facile hydrothermal and electrodeposition processes. Due to the ultrathin NiCo-LDH layer, the change in the local electronic structure resulting from the interaction of two components can be effectively transferred to the surface of electrocatalysts, which was verified by XPS tests. The heterostructure exhibits excellent activity and stability as efficient bifunctional electrocatalysts for overall water splitting. The corresponding overpotentials are 270 mV at 50 mA cm-2 for the oxygen evolution reaction (OER), and 93 mV at 10 mA cm-2 for the hydrogen evolution reaction (HER) in 1.0 M KOH, respectively. It is noteworthy that the OER activity exceeds that of RuO2. Meanwhile, the heterostructure presents excellent stability for more than 40 hours. The outstanding performance is attributed to the surface electronic structure of NiCo-LDH optimized by highly conductive and stable CuNiCo trimetallic spinel sulfides. The results confirm that it is an effective strategy to tune the catalytic performance by constructing a heterostructure with an ultrathin surface layer.

Flower-like 1T-MoS2/NiCo2S4 on a carbon cloth substrate as an efficient electrocatalyst for the hydrogen evolution reaction.

The 1T-MoS2/NiCo2S4 composite in situ grown on carbon cloth (CC) was successfully prepared by a two-step hydrothermal method as an efficient electrode for the hydrogen evolution reaction. The morphology and composition characterization show that the composite has a flower-like structure with a large number of edges and surfaces exposed, and the content of the 1T phase in MoS2 is 63%. 1T-MoS2/NiCo2S4/CC exhibits an overpotential of 107 mV at 10 mA cm-2, and a Tafel slope of 66.4 mV dec-1 in an alkaline electrolyte. After continuous electrolysis for 24 h at an overpotential of 170 mV, 86% of the original current density was retained in an chronoamperometry measurement. The outstanding catalytic performance of the composite is ascribed to its unique structure, high 1T-MoS2 content and the synergistic catalysis between 1T-MoS2 and NiCo2S4. This work provides a facile and effective strategy for fabricating the 1T-MoS2/NiCo2S4/CC composite and demonstrates that the composite is expected to be a competitive non-noble HER catalyst.