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Nano-MgO carbon composites (MCs) demonstrated great potential in phosphate immobilization to resolve phosphorus reuse and eutrophication problems, but the mechanisms of phosphate immobilization are still unclear. In this study, MCs were fabricated via CO2 activation of hydrochar materials, and the activation mechanisms were first investigated through analysis of pyrolysis gases and porosity. The results indicate that MgO particles (pyrolysis products of MgCl2) catalyzed the consumption of the carbon matrix but blocked the development of carbon matrix pores. Furthermore, phosphate immobilization by MCs increased with the increase of MgO loading content. More importantly, XPS and TEM-EDX profiles demonstrate that solution and surface precipitations regulated phosphate immobilization by MCs. Solution precipitation mainly contributed to a MgHPO4 precipitate, while in surface precipitation the carbon matrix served as a bridge for H2PO4− transmission to MgO particles to produce a Mg(H2PO4)2 precipitate. Also, with the decrease of carbon content, surface precipitation became dominant due to the shortened distance. This contributes to the improvement of phosphate immobilization by MCs, which was found to be even higher than pure MgO. Compared with N2 activated MC, CO2 activated MC showed much higher phosphate immobilization potential attributed to the surface precipitation reaction. The results of this study will guide the development of more efficient MC materials for phosphate recovery.

Cesium lead iodide perovskite (CsPbI3) has been proposed as an efficient alternative to modify the instability of methylammonium lead iodide (MAPbI3) under thermal and humidity stress. However, three-dimensional (3D) cesium lead iodide forms an undesirable non-perovskite structure with a wide bandgap at ambient atmosphere. Herein, dimension engineering is employed by introducing a bulky ammonium cation to form stable 2D cesium lead iodide perovskite BA2CsPb2I7 (BA = CH3(CH2)3NH3), which not only exhibits prominent optoelectronic properties, but also possesses superior structural and compositional stability to 3D CsPbI3 and MAPbI3 under the pressure of heat and humidity. The current 2D BA2CsPb2I7 shows excellent stability after exposure to 30% relative humidity for 30 days or upon heating at 85 °C for 3 days. In addition, the corresponding BA2CsPb2I7 based planar perovskite solar cells retain 92% of the initial power conversion efficiency (PCE) after aging for over 30 days without any encapsulation, demonstrating the up-scalability of 2D perovskite compounds as stable and efficient light-absorbing materials for perovskite solar cells and other optoelectronic applications.

Halide perovskite single crystal of cubic HC(NH2)2PbI3 (FAPbI3) having excellent optoelectronic properties, such as narrow bandgap, large absorption coefficient and superior thermal stability has caught a surge of attention as a promising material for production of high-performance optoelectronic devices. However, at room temperature, the self-transformation of cubic FAPbI3 perovskite phase to non-perovskite phase leaves a critical roadblock to its practical viability. Herein, a simple alloying strategy by mixing methylammonium with formamidinium is developed to stabilize the FAPbI3 perovskite phase, hence achieving a highly stable mixed cation MA0.45FA0.55PbI3 perovskite single crystal over a span of 14 months. The MA0.45FA0.55PbI3 single crystal exhibits exceptional optoelectronic properties like high carrier mobility of 271 ± 60 cm2 s−1 V−1 and long diffusion length up to 254 μm, which are twice the values for sole MAPbI3 or FAPbI3 crystals. In addition, the photodetector based on MA0.45FA0.55PbI3 single crystal exhibits low detection limit of about 1 nW cm−2, high ON–OFF ratio of ∼1000, short response time of less than 200 μs, and impressive stability under aging in dark for 4 months or continuous photo-switching test for 1000 s.

Designing and exploring efficient and stable non-noble bifunctional catalysts by nanostructure modification and chemical composition tuning for water splitting is of critical importance for sustainable resources. Herein, pure phase nickel molybdenum phosphide (NiMoP2) nanowires on carbon cloth are successfully synthesized through a simple and highly reproducible in situ P/O exchange process. Such a NiMoP2 nanowire catalyst requires low overpotentials of 199 and 330 mV to obtain a high current density of 100 mA cm−2 towards the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, and is among the most active HER and OER electrocatalysts yet reported. The bifunctional NiMoP2 is used as both anode and cathode catalysts in a two-electrode water electrolysis configuration, which delivers a current density of 10 mA cm−2 under a potential of 1.67 V. Furthermore, the overall water-splitting of the bifunctional NiMoP2 nanowire catalyst is further driven by a dry battery with a nominal voltage of 1.5 V which exhibits excellent performance and durability in a strong alkaline electrolyte.

The power conversion efficiency (PCE) of a planar perovskite solar cell (PSC) is closely associated with the conduction band energy, conductivity and coverage of the compact layer. However, as the most widely used compact layer material, TiO2 has unfavorable electrical properties such as low electron mobility and conductivity; as a result, modifications such as elemental doping are of paramount importance. In this study, Nb-doped TiO2 with improved carrier density and conductivity was prepared via a facile one-pot solution process and applied successfully as a high-quality compact layer for planar PSCs. A positive shift in the flat-band potential (Vfb) and increased conductivity after Nb doping efficiently facilitated photogenerated electron injection and charge extraction from the perovskite film to the 2% Nb-doped TiO2 compact layer, contributing to impressive advances in photovoltaic performance compared with pristine TiO2. Ultimately, a PSC assembled using optimized 2% Nb-doped TiO2 and CH3NH3PbI3 yielded a power conversion efficiency of up to 16.3%.

In situ fabrication of an ordered macroporous perovskite semitransparent film on a FTO glass was successfully achieved via sacrificial polystyrene (PS) microsphere templates. The average visible transmittance of active layer from 20% to 45% can be tuned by simply changing the PS diameters and precursor concentrations. The ordered macroporous perovskite films show enhanced crystallinity and reduced recombination defects, superior to the island perovskite film. Transient photovoltage, transient photocurrent and electrochemical impedance spectra measurements proved the advanced charge transport and reduced recombination by importing macroporous structures. Herein, the optimized 400 nm MP CH3NH3PbI3 perovskite film with a high AL AVT of 36.5% achieved an impressive PCE of 11.7% compared to the island-like perovskite film (champion PCE = 5.6%), presenting a great potential for building integrated photovoltaic applications.

Solar water splitting by photoelectrochemical (PEC) cells is emerged as a promising route for H2 production. However, thus far no single component material can fulfill all the requirements for high efficiency PEC behavior, especially for the photoanode which conducts the water oxidation, while constructing a composite photoelectrode can result in improved performance. Herein, a simple wet-chemical treatment method is introduced to in situ fabricate ZnFe2O4 onto conductive Al:ZnO nanowire arrays for solar-driven water splitting. Benefiting from the high conductivity of Al:ZnO and the visible-spectrum absorption of ZnFe2O4, such a host–guest structure has finally led to an excellent photoelectrochemical performance with low onset potential (VRHE = 0.38 V) and a photocurrent density of 1.72 mA cm−2 (VRHE = 1.23 V). Notably, the low onset potential gives this structure great potential for application in unassisted light-driven tandem-type PEC cells.

The ingenious design of nanostructures and smart integration of specific semiconducting metal oxide materials are closely related to the photovoltaic performance of solar cells. Herein, we successfully fabricate vertically aligned TiO2 nanowire–TiO2 nanosheet–ZnO nanorod (TNW–TNS–ZNR) hyperbranched heterostructured arrays on TCO substrates as excellent anode material electrodes for efficient solar-to-electricity conversion. As a result, the TNW–TNS–ZNR heterostructured array based quantum dot-sensitized solar cells (QDSSCs) have exhibited an improved power conversion efficiency (PCE) under AM 1.5G one sun illumination, along with considerable improvement of short-circuit current density (Jsc), open voltage (Voc) and fill factor (FF) due to their superior light harvesting and excellent charge collection capability. Combined with the chemical bath deposited Cu2S counter electrode, the eventual PCE of CdS/CdSe co-sensitized solar cells can be further boosted to as high as 5.38%.

Metal–organic skeleton based gel electrolytes are prepared for the first time for high efficiency quasi-solid-state DSSCs. The gel electrolytes feature in their sponge-like porous matrix of a metal–organic gel (MOG) assembled by coordination of Al3+ and 1,3,5-benzenetricarboxylate (H3BTC), which can provide an excellent ability to accommodate electrolyte ingredients, thus largely preserving the properties of the liquid electrolyte. Meanwhile, the MOG electrolyte can well penetrate into the photoanode film to ensure a good interfacial contact. The effects of the concentration of active species in the MOG electrolyte on the photoelectrical performances are investigated. On increasing the concentration, Jsc of gel-state cells improves gradually due to the enhanced I−/I3− redox couple content, while Voc undergoes an increase first but decreases subsequently. The synergistic function of cations (such as Al3+, Li+, etc.) and tert-butylpyridine (TBP), which can induce a conductive band (CB) shift of the TiO2 photoanode and affect the electron recombination, may contribute to the variation of Voc. By optimizing the composition of the gel electrolyte, a high conversion efficiency of over 8.60% can be obtained, which is a little lower than that of a liquid-state cell (9.13%). This research study will open up a new way to fabricate quasi-solid-state DSSCs with high efficiency.