Unraveling the crucial contribution of additive chromate to efficient and stable alkaline seawater oxidation on Ni-based layered double hydroxides

Seawater electrolysis to generate hydrogen offers a clean, green, and sustainable solution for new energy. However, the catalytic activity and durability of anodic catalysts are plagued by the corrosion and competitive oxidation reactions of chloride in high concentrations. In this study, we find that the additive CrO42- anions in the electrolyte can not only promote the formation and stabilization of the metal oxyhydroxide active phase but also greatly mitigate the adverse effect of Cl- on the anode. Linear sweep voltammetry, accelerated corrosion experiments, corrosion polarization curves, and charge transfer resistance results indicate that the addition of CrO42- distinctly improves oxygen evolution reaction (OER) kinetics and corrosion resistance in alkaline seawater electrolytes. Especially, the introduction of CrO42- even in the highly concentrated NaCl (2.5 M) electrolyte prolongs the durability of NiFe-LDH to almost five times the case without CrO42-. Density functional theory calculations also reveal that the adsorption of CrO42- can tune the electronic configuration of active sites of metal oxyhydroxides, enhance conductivity, and optimize the intermediate adsorption energies. This anionic additive strategy can give a better enlightenment for the development of efficient and stable oxygen evolution reactions for seawater electrolysis.

Unraveling the Oxidation Kinetics Through Electronic Structure Regulation of MnCo2O4.5@Ni3S2 p-n Junction for Urea-Assisted Electrocatalytic Activity

A promising strategy to boost electrocatalytic performance is via assembly of hetero-nanostructured electrocatalysts that delivers the essential specific surface area and also active sites by lowering the reaction barrier. However, the challenges associated with the intricate designs and mechanisms remain underexplored. Therefore, the present study constructs a p-n junction in a free-standing MnCo2O4.5@Ni3S2 on Ni-Foam. The space-charge region's electrical characteristics is dramatically altered by the formed p-n junction, which enhances the electron transfer process for urea-assisted electrocatalytic water splitting (UOR). The optimal MnCo2O4.5@Ni3S2 electrocatalyst results in greater oxygen evolution reactivity (OER) than pure systems, delivering an overpotential of only 240 mV. Remarkably, upon employing as UOR electrode the required potential decreases to 30 mV. The impressive performance of the designed catalyst is attributed to the enhanced electrical conductivity, greater number of electrochemical active sites, and improved redox activity due to the junction interface formed between p-MnCo2O4.5 and n-Ni3S2. There are strong indications that the in situ formed extreme-surface NiOOH, starting from Ni3S2, boosts the electrocatalytic activity, i.e., the electrochemical  surface reconstruction generates the active species. In conclusion, this work presents a high-performance p-n junction design for broad use, together with a viable and affordable UOR electrocatalyst.

d-Band Center Optimization of Ti3C2Tx MXene Nanosheets for Ultrahigh NO2 Gas Sensitivity at Room Temperature

MXene exhibits numerous advantageous properties such as high electronic conductivity, high surface area, and ease of surface modification via tailoring of functional groups. However, the mechanism by which MXene functionalization enhances gas sensing performance has not yet been well understood, let alone the development of a rational sensor design optimization strategy. This work presents a functionalization methodology for MXene based on d-band center modulation, which can be implemented by introducing Fe onto the surface of Ti3C2Tx nanosheets, for significantly improved gas sensing response and selectivity. The strategy is demonstrated in the design of gas sensors. The optimized gas sensor shows a response of 50% toward 10 ppm of NO2 at room temperature, which is over 6-fold improvement from its pristine counterpart, an unprecedented performance level among all reported MXene gas sensors. XPS characterizations, valence band analyses, and density functional theory (DFT) calculations all indicate that the underlying enhancement mechanism can be attributed to the tuning of the d-band center energy toward the Fermi level. This work provides a new design strategy based on the optimization of the d-band center energy and adds a much needed systematic and quantitative method to the design of two-dimensional materials based semiconducting gas sensors.

Order-disorder engineering of RuO2 nanosheets towards pH-universal oxygen evolution

Ru-based electrocatalysts are considered promising anode catalysts towards water electrolysis due to their impressive activity under acidic conditions. Yet, caused by the collapse of the local crystalline domains and concurrent leaching of Ru species during the OER process, durability against structural degradation remains poor. Herein, we present an order-disorder structure optimization strategy, based on RuO2 nanosheets with well-defined amorphous-crystalline boundaries supported on carbon cloth (a/c-RuO2/CC), to effectively catalyze water oxidation, especially in the case of an acidic medium. Specifically, the as-prepared a/c-RuO2/CC sample has achieved a lower overpotential of 150 mV at 10 mA cm-2, a smaller Tafel slope of 47 mV dec-1, and a significantly higher durability with suppressed dissolution of Ru, with regard to its crystalline (c-RuO2/CC) and amorphous (a-RuO2/CC) counterparts. Computational simulations combined with experimental characterizations uncover that the construction of the structurally ordered-disordered boundary enables a weakened Ru-O covalency with regard to the ordered counterpart, which suppresses the leaching of active Ru species from the crystalline phase, thus enhances stability. An upshift of the d-band center in a/c-RuO2/CC relative to a-RuO2/CC reduces the energy barrier of the potential-determining step (*O → *OOH), thereby dramatically boosting activity.

Recent Progress of Metal Sulfide Photocatalysts for Solar Energy Conversion

Artificial photosynthetic solar-to-chemical cycles enable an entire environment to operate in a more complex, yet effective, way to perform natural photosynthesis. However, such artificial systems suffer from a lack of well-established photocatalysts with the ability to harvest the solar spectrum and rich catalytic active-site density. Benefiting from extensive experimental and theoretical investigations, this bottleneck may be overcome by devising a photocatalytic platform based on metal sulfides with predominant electronic, physical, and chemical properties. These tunable properties can endow them with abundant active sites, favorable light utilization, and expedited charge transportation for solar-to-chemical conversion. Here, it is described how some vital lessons extracted from previous investigations are employed to promote the further development of metal sulfides for artificial photosynthesis, including water splitting, CO₂ reduction, N₂ reduction, and pollutant removal. Their functions, properties, synthetic strategies, emerging issues, design principles, and intrinsic functional mechanisms for photocatalytic redox reactions are discussed in detail. Finally, the associated challenges and prospects for the utilization of metal sulfides are highlighted and future development trends in photocatalysis are envisioned.