The possibility of lead (Pb) contamination and the volatility of the organic cations in the prevailing Pb-based organic-inorganic perovskite (HP) light absorbers are the two key issues of concern in the emerging perovskite solar cells (PSCs). The majority of the Pb-free HP candidates that are being explored for PSCs either suffer from instability issues and have unfavorable defect properties or have unsuitable bandgaps for PSC applications. We report the prediction of a promising new family of all-inorganic HPs based on the nontoxic, earth-abundant, ultrastable Ti­(IV) for use in PSCs. We show that the Ti-based HPs possess a combination of several desirable attributes, including suitable bandgaps, excellent optical absorption, benign defect properties, and high stability. In particular, we show experimentally that representative members of the Ti-based HP family, Cs2TiI x Br6–x , have bandgaps that can be tuned between the ideal values of 1.38 and 1.78 eV for single-junction and tandem photovoltaic applications, respectively.

Boosting ammonia with a little oxygen Ammonia synthesis from nitrogen for fertilizer production is highly energy intensive. Chemists are therefore exploring electrochemical approaches that could draw power from renewable sources while generating less waste. One promising cycle involves the reduction of lithium ions at an electrode, with the resultant metal in turn reducing nitrogen and regenerating the ions. Li et al . report the counterintuitive result that small quantities of oxygen could enhance the efficiency of this process, which they attribute to diffusional effects that limit excessive lithium reduction. —JSY

Ammonia is a critical component in fertilizers, pharmaceuticals, and fine chemicals and is an ideal, carbon-free fuel. Recently, lithium-mediated nitrogen reduction has proven to be a promising route for electrochemical ammonia synthesis at ambient conditions. In this work, we report a continuous-flow electrolyzer equipped with 25–square centimeter–effective area gas diffusion electrodes wherein nitrogen reduction is coupled with hydrogen oxidation. We show that the classical catalyst platinum is not stable for hydrogen oxidation in the organic electrolyte, but a platinum-gold alloy lowers the anode potential and avoids the decremental decomposition of the organic electrolyte. At optimal operating conditions, we achieve, at 1 bar, a faradaic efficiency for ammonia production of up to 61 ± 1% and an energy efficiency of 13 ± 1% at a current density of −6 milliamperes per square centimeter.

No abstract