Monitoring surface dynamics of electrodes during electrocatalysis using in situ synchrotron FTIR spectroscopy

Isolated iridium oxide sites on modified carbon nitride for photoreforming of plastic derivatives

The rising concentration of plastics due to extensive disposal and inefficient recycling of plastic waste poses an imminent and critical threat to the environment and ecological systems. Photocatalytic reforming of plastic derivatives to value-added chemicals under ambient conditions proceeds at lower oxidation potential which galvanizes the hydrogen evolution. We report the synthesis of a narrow band gap NCN-functionalized O-bridged carbon nitride (MC) through condensation polymerization of hydrogen-bonded melem (M)-cyameluric acid (C) macromolecular aggregate. The MC scaffold hosts well-dispersed Ir single atom (MCIrSA) sites which catalyze oxidative photoreforming of alkali-treated polylactic acid (PLA) and polyethylene terephthalate (PET) derivatives to produce H2 at a rate of 147.5 and 29.58 μmol g-1cat h-1 under AM1.5G irradiation. Solid-state electron paramagnetic resonance (EPR) and time-resolved photoluminescence (TRPL) reveals efficient charge carrier generation and separation in MCIrSA. X-ray absorption spectroscopy (XAS) and Bader charge analysis reveal undercoordinated IrN2O2 SA sites pinned in C6N7 moieties leading to efficient hole quenching. The liquid phase EPR, in situ FTIR and density functional theory (DFT) studies validate the facile generation of •OH radicals due to the evolution of O-Ir-OH transient species with weak Ir--OH desorption energy barrier.

Atomic Ru Species Driven SnO2-Based Sensor for Highly Sensitive and Selective Detection of H2S in the ppb-Level

Timely and accurate detection of H2S is crucial for preventing serious health issues in both humans and livestock upon exposure. However, metal-oxide-based H2S sensors often suffer from mediocre sensitivity, poor selectivity, or long response/recovery time. Here, an atomic Ru species-driven SnO2-based sensor is fabricated to realize highly sensitive and selective detection of H2S at the parts per billion level as low as 100 ppb. The sensor shows a high sensing response (Rair/Rgas = 310.1) and an ultrafast response time (less than 1 s) to 20 ppm H2S at an operating temperature of 160 °C. Operando SR-FTIR spectroscopic characterizations and DFT calculations prove that the superior sensing properties can be mainly attributed to the driven effect of atomic Ru species on the formation of surface-adsorbed oxygen species on the surface of SnO2, which provides more active sites and enhances the sensing performance of SnO2 for H2S. Furthermore, a lab-made wireless portable H2S monitoring system is developed to rapidly detect the H2S for early warning, suggesting the potential application of the fabricated H2S sensor and monitoring system. This work provides a novel approach for fabricating a highly sensitive and selective gas sensor driven by atomic metal species loaded on metal-oxide semiconductors.

Tensile straining of iridium sites in manganese oxides for proton-exchange membrane water electrolysers

Although the acidic oxygen evolution reaction (OER) plays a crucial role in proton-exchange membrane water electrolysis (PEMWE) devices, challenges remain owing to the lack of efficient and acid-stable electrocatalysts. Herein, we present a low-iridium electrocatalyst in which tensile-strained iridium atoms are localized at manganese-oxide surface cation sites (TS-Ir/MnO2) for high and sustainable OER activity. In situ synchrotron characterizations reveal that the TS-Ir/MnO2 can trigger a continuous localized lattice oxygen-mediated (L-LOM) mechanism. In particular, the L-LOM process could substantially boost the adsorption and transformation of H2O molecules over the oxygen vacancies around the tensile-strained Ir sites and prevent further loss of lattice oxygen atoms in the inner MnO2 bulk to optimize the structural integrity of the catalyst. Importantly, the resultant PEMWE device fabricated using TS-Ir/MnO2 delivers a current density of 500 mA cm-2 and operates stably for 200 h.