Organic-inorganic lead halide perovskite phases segregate (and their structures degrade) under illumination, exhibiting a poor stability with hysteresis and producing halide accumulation at the surface.In this work, we observed structural and interfacial dissociation in methylammonium lead iodide (CH NH PbI ) perovskites even under dark and vacuum conditions. Here, we investigate the origin and consequences of self-degradation in CH NH PbI perovskites stored in the dark under vacuum. Diffraction and photoelectron spectroscopic studies reveal the structural dissociation of perovskites into PbI , which further dissociates into metallic lead (Pb ) and I ions, collectively degrading the perovskite stability. Using TOF-SIMS analysis, AuI formation was directly observed, and it was found that an interplay between CH NH , I , and mobile I ions continuously regenerates more I ions, which diffuse to the surface even in the absence of light. Besides, halide diffusion causes a concentration gradient between Pb and I and creates other ionic traps (PbI , PbI ) that segregate as clusters at the perovskite/gold interface. A shift of the onset of the absorption band edge towards shorter wavelengths was also observed by absorption spectroscopy, indicating the formation of defect species upon aging in the dark under vacuum.

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Manganese-based electrocatalyst has a great attention for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) applications, since the discovery of active centre in nature photosynthesis system. The Mn oxidation state optimization and structural defect engineering are essential to get a highly active Mn-based catalytic materials. MnP showed a good water oxidation activity with a lower overpotential of 286 mV to reach the current density of 10 mA/cm 2 and a Tafel slope of 76 mV/ dec. Also, the electron transfer number calculated from both the rotating disk electrode and rotating ring-disk electrode techniques is a quasi-4 electron transfer process with an onset and halfwave potential of 0.998 V and 0.936 V vs RHE respectively. MnP achieved a higher limiting kinetic current of 5.7 mA/cm 2 and a very low H 2 O 2 yield of 1.6 %. Chronoamperometry and cyclic voltammetry studies confirmed the long-term stability and durability of the prepared catalyst. The variance metrics ΔE [Ej 10 À Ej -3 ] is used to estimate the overall activity from the potential difference between OER overpotential at 10 mA/cm 2 and ORR kinetic current at 3 mA/cm 2 . MnP shows very low ΔE (0.58 V) which demonstrate an efficient bifunctional activity in ORR and OER reactions. This work might shed new light on the development of MnP based bifunctional oxygen electrocatalyst.

The quest for the development of promising electrode materials for energy storage persists.