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Manganese(II)-doped cesium–lead–chloride (Mn2+:CsPbCl3) perovskite nanocrystals have recently been developed as promising luminescent materials and attractive candidates for white-light generation. One approach to tuning the luminescence of these materials has involved anion exchange to incorporate Br–, but the effects of anion exchange on Mn2+speciation in doped metal-halide perovskites is not well understood at a microscopic level. Here, we use a combination of X-band electron paramagnetic resonance (EPR) and photoluminescence spectroscopies to monitor the Mn2+dopants in Mn2+:CsPbCl3nanocrystals during Cl–→ Br–anion exchange. Analytical measurements show that the nanocrystals retain their Mn2+over the course of Cl–→ Br–anion exchange and they continue to show strong Mn2+d–dluminescence but, surprisingly, the Mn2+EPR intensities all but vanish. Further results suggest that Mn2+ions migrate during anion exchange to form clusters that are still luminescent but show no EPR signal due to antiferromagnetic superexchange coupling. Monte Carlo simulation and analysis of the Mn2+:CsPb(Cl1–xBrx)3lattice at various halide compositions (x) bolsters this interpretation by indicating a propensity for Mn2+–Cl–units to cluster as the Br–content increases, increasing the probability of the nearest-neighbor Mn2+–Mn2+interactions. The driving force for this clustering is retention of the stronger Mn–Cl bonds compared to Mn–Br bonds. In addition, modeling predicts spinodal decomposition to form Mn2+-enriched domains even at the end point compositions of x= 0 and 1, with Mn2+ordering in next-nearest-neighbor positions driven by Coulomb interactions and lattice-strain minimization. These results have important implications for both fundamental studies and applications of doped and alloyed metal-halide perovskites.

In-use exhaust stream CH4emissions from two dual fuel marine engines were characterized and strategies for CH4reduction were identified and evaluated. For this, a low-cost, portable, wavelength modulation spectroscopy (WMS) system was developed. The performance of the developed WMS sensor was assessed using gas standards and demonstrated on a heavy-duty, diesel pilot ignited, direct-injection natural gas research engine through comparison to a flame ionization detector. The WMS sensor was subsequently used to measure the exhaust-stream CH4concentration from two diesel pilot-ignited, port-injected natural gas engines on a coastal vessel while under normal operation. Using cylinder deactivation to reduce the excess air ratio, λ, and vessel operation changes to minimize operation at lower loads, the total CH4emission were reduced by up to 33%. The measured, load specific CH4emissions were subsequently used to identify an improved vessel operation strategy, with an estimated 56–60% reduction in CH4emissions. These results demonstrate the importance of considering the real-world engine operation profile for accurate estimates of the global warming potential, as well as the utility of a WMS sensor for characterizing and mitigating in-use CH4emissions.

The photoconversion of CO2to hydrocarbons is a sustainable route for its transformation into value-added compounds, which is crucial to mitigating energy and climate crises. CuPt nanoparticles on TiO2surfaces have been reported to show promising photoconversion efficiencies. For further progress, a mechanistic understanding of the catalytic properties of these CuPt/TiO2systems is vital. Here, we employ ab initiocalculations, machine learning, and photocatalysis experiments to understand the photocatalytic reduction of CO2on CuPt/TiO2. We explore the configurational space of the CO2@CuPt/TiO2systems and examine their structures and energetics. We find that the CuPt/TiO2interface plays a key role in determining CO2activation and, thus, the conversion to hydrocarbons. The interface stabilizes *CO and other intermediates containing CH groups, thus facilitating a higher activity and selectivity for methane. A bias-corrected machine-learning interatomic potential trained on density functional theory data enables the efficient exploration of the potential energy surfaces of numerous CO2@CuPt/TiO2configurations using basin-hopping Monte Carlo simulations, greatly accelerating the study of these photocatalyst systems. Our simulations show that CO2preferentially adsorbs at the interface, with a C atom bonded to a Pt site and one O atom occupying an O-vacancy site. The interface also promotes the formation of *CH and *CH2intermediates. For confirmation, we synthesize CuPt/TiO2samples with various compositions, analyze their morphologies and compositions using scanning electron microscopy and energy-dispersive X-ray spectroscopy, and measure their photocatalytic activity. Our computational and experimental findings qualitatively agree and highlight the importance of the interface design for the selective conversion of CO2to hydrocarbons.

Reviewer: David W. Sommer, University of Georgia Employee benefits is a dynamic, rapidly evolving field. Anyone who has worked or taught in this area knows the challenges of staying current [...]