Perovskite synthesis out in the open: Although methods have been developed that create the photoactive black perovskite phase of formamidinium lead iodide (α-FAPbI ₃ ), these routes are temperature and humidity sensitive and less compatible with large-scale solar cell production. Hui et al. report an alternative route in which vertically aligned lead iodide thin films are grown from the ionic liquid methylamine formate. Nanoscale channels in the films lower the barrier to permeation of formamidinium iodide and enable transformation to α-FAPbI ₃ , even at high humidity and room temperature. Solar cells made with these films have power conversion efficiencies as high as 24.1% that display high stability. Science , this issue p. 1359

Energy storage is a very significant issue for utilization of solar energy due to its discontinuous and unstable energy flux. Herein, for the first time, we propose a Fe₂O₃@Ni(OH)₂ core–shell nanorod array as a photoelectrochemical battery-type supercapacitor for the direct storage of solar energy. Under light illumination, Fe₂O₃ absorbs solar energy and produces electron–hole pairs, while Ni(OH)₂ stores the photo-generated holes, which can be released as electricity when the light is switched off. In addition, by controlling the valence band position of the semiconductor and the thickness of Ni(OH)₂, the side reaction of water oxidation (electrolyte decomposition), which is harmful for the applications of a photoelectrochemical supercapacitor, can be completely suppressed. As a consequence, the specific capacitance of the Fe₂O₃@Ni(OH)₂ photoelectrochemical supercapacitor is enhanced up to 20.6 mF cm⁻² at a discharge current density of 0.1 mA cm⁻², which is about 4.5 times that of BiVO₄/PbO_x reported in a previous study. This study offers a very promising device for the direct storage of solar energy and deepens our understanding on the interface charge transfer between a photoelectrode and a battery-type capacitive material.

Atomic valence state regulation is an advantageous approach for improving photocatalytic efficiency and product selectivity. However, it is difficult to precisely control the ratio of the different valence states on the surface and the relationship between the surface valence change and catalytic efficiency in the photocatalytic reaction process is unclear. Herein, CeVO₄ ultrathin nanosheets were fabricated by one-step solvothermal method with ethanolamine (MEA) as the structure-directing agent. The ratio of the concentrations of intrinsic Ce⁴⁺ and Ce³⁺ ions is precisely modulated from 19.82:100 to 13.33:100 changed by the volume of MEA added without morphology modification. The photocatalytic efficiency increases as the concentrations of intrinsic Ce⁴⁺ and Ce³⁺ ions decrease and CV3 (prepared with 3 mL of MEA) shows the highest CO generation rate approximately 6 and 14 times larger than CV (prepared without MEA) and CV1 (prepared with 1 mL of MEA), respectively, in the photocatalytic CO₂ reduction. Interestingly, about 6.8% photo-induced Ce⁴⁺ ions were generated on the surface of the catalysts during the photocatalytic CO₂ reduction without any phase and morphology changes for CV3. The photocatalytic reaction mechanism is proposed considering the intrinsic and photo-induced Ce⁴⁺ ions to obtain efficient photocatalysts.

A fascinating Bi ₂ MoO ₆ homojunction (HJ) array vertically grown on an FTO substrate was built up through a convenient one-step route; the array consisted of ultrathin nanosheet (NS)-anchored hexahedral prismatic nanorods (NR).

Copper-based electrodes can catalyze electroreduction of CO₂ to two-carbon products. However, obtaining a specific product with high efficiency depends on the oxidation state of Cu for the Cu-based materials. In this study, Cu-based electrodes were prepared on fluorinated tin oxide (FTO) using the one-step electrodeposition method. These electrodes were used as efficient electrocatalysts for CO₂ reduction to ethanol. The concentration ratio of Cu⁰ and Cu⁺ on the electrodes was precisely modulated by adding monoethanolamine (MEA). The results of spectroscopic characterization showed that the concentration ratio of localized Cu⁺ and Cu⁰ (Cu⁺/Cu⁰) on the Cu-based electrodes was controlled from 1.24/1 to 1.54/1 by regulating the amount of MEA. It was found that the electrode exhibited the best electrochemical efficiency and ethanol production in the CO₂ reduction reaction at the optimal concentration ratio Cu⁺/Cu⁰ of 1.42/1. The maximum faradaic efficiencies of ethanol and C₂ were 48% and 77%, respectively, at the potential of −0.6 V vs. a reversible hydrogen electrode (RHE). Furthermore, the optimal concentration ratio of Cu⁺/Cu⁰ achieved the balance between Cu⁺ and Cu⁰ with the most favorable free energy for the formation of *CO intermediate. The stable existence of the *CO intermediate significantly contributed to the formation of the C–C bond for ethanol production.