Quality-dependent performance of hydrophobic ZIF-67 upon high-pressure water intrusion-extrusion process

Zeolitic imidazolate framework (ZIF) microporous materials have already been employed in many fields of energetic and environmental interest since the last decade. The commercial scale production of some of these materials makes them more accessible for their implementation in industrial processes; however, their massive synthesis may entail modifications to the preparation protocols, which may result in a loss in the optimization of this process and a drop in the material's quality. This fact may have implications for the performance of these materials during their lifetime, especially when they are used in applications such as energy dissipation, in which they are subjected to several operating cycles under high pressures. This study focuses on ZIF-67, a material that has demonstrated in the past its ability to dissipate energy through the water intrusion-extrusion process under high pressure. Two ZIF-67 samples were synthesized using different protocols, and 2 batches of different qualities (labelled as high quality (HQ) and low quality (LQ)) were obtained and analysed by water porosimetry to study their performance in the intrusion-extrusion process. Unexpectedly, minor structural differences, which are typically neglected especially under production conditions, had a dramatic effect on their performance. The results presented in this study reiterate the importance of quality control with respect to reproducibility of experimental results. In a broader perspective, they are critical to the technology transfer from academia to industry.

Facet Control of Nickel Nitride Nano-Framework for Efficient Hydrogen Evolution Electrocatalysis via Auxiliary Cooling Assisted Plasma Engineering

The precise facet modulation of transition metal nitrides (TMNs) has been regarded as an essential issue in boosting electrocatalytic H₂ production. Compared to thermal nitridation, the plasma technique serves as a favorable alternative to directly achieve TMNs, but the apparent surface heating effect during plasma treatment inevitably causes the thermally stabilized nitride formation, resulting in the deterioration of the highly reactive facet. To optimize the hydrogen evolution reaction (HER) behavior, an auxiliary cooling assisted plasma system to selectively expose Ni₃ N (2-10) with favorable activity by controlling surface heating during plasma nitridation is designed. The resultant nickel nitride (cp-Ni₃ N) nano-framework delivers exceptional catalytic performance, evidenced by its low overpotential of 58 and 188 mV at the current density of 10 and 100 mA cm^-2 for HER, in stark comparison with that of normal plasma and thermally fabricated Ni₃ N. Operando plasma diagnostics along with numerical simulation further confirm the effect of surface heating on typical plasma parameters as well as the Ni₃ N nanostructure, indicating the key factor responsible for the high-performance nitride electrocatalyst.

Realizing Interfacial Electron/Hole Redistribution and Superhydrophilic Surface through Building Heterostructural 2 nm Co0.85 Se-NiSe Nanograins for Efficient Overall Water Splittings

Electrochemical overall water splitting using renewable energy input is highly desirable for large-scale green hydrogen generation, but it is still challenged due to the lack of low-cost, durable, and highly efficient electrocatalysts. Herein, 1D nanowires composed of numerous 2 nm Co_0.85 Se-NiSe nanograin heterojunctions as efficient precious metal-free bifunctional electrocatalyst are reported for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution with the merits of high activity, durability, and low cost. The abundant microinterface among the ultrafine nanograins and the presence of lattice distortion around nanograin interface is found to create a superhydrophilic surface of the electrocatalyst, which significantly facilitate the fast diffusion of electrolytes and the release of the formed H₂ and O₂ from the catalyst surface. Furthermore, synergic effect between Co_0.85 Se and NiSe grain on adjusting the electronic structure is revealed, which enhances electron mobility for fast electron transport during the HER/OER process. Owing to these merits, the rationally designed Co_0.85 Se-NiSe heterostructures display efficient overall water splitting behavior with a low voltage of 1.54 V at 10 mA cm^-2 and remarkable long-term durability for the investigated period of 50 h.

Artificial Heterointerfaces Achieve Delicate Reaction Kinetics towards Hydrogen Evolution and Hydrazine Oxidation Catalysis

Electrochemical water splitting for H₂ production is limited by the sluggish anode oxygen evolution reaction (OER), thus using hydrazine oxidation reaction (HzOR) to replace OER has received great attention. Here we report the hierarchical porous nanosheet arrays with abundant Ni₃ N-Co₃ N heterointerfaces on Ni foam with superior hydrogen evolution reaction (HER) and HzOR activity, realizing working potentials of -43 and -88 mV for 10 mA cm^-2 , respectively, and achieving an industry-level 1000 mA cm^-2 at 200 mV for HzOR. The two-electrode overall hydrazine splitting (OHzS) electrolyzer requires the cell voltages of 0.071 and 0.76 V for 10 and 400 mA cm^-2 , respectively. The H₂ production powered by a direct hydrazine fuel cell (DHzFC) and a commercial solar cell are investigated to inspire future practical applications. DFT calculations decipher that heterointerfaces simultaneously optimize the hydrogen adsorption free energy (ΔG_H* ) and promote the hydrazine dehydrogenation kinetics. This work provides a rationale for advanced bifunctional electrocatalysts, and propels the practical energy-saving H₂ generation techniques.

Manipulating dehydrogenation kinetics through dual-doping Co3N electrode enables highly efficient hydrazine oxidation assisting self-powered H2 production

Replacing sluggish oxygen evolution reaction (OER) with hydrazine oxidation reaction (HzOR) to produce hydrogen has been considered as a more energy-efficient strategy than water splitting. However, the relatively high cell voltage in two-electrode system and the required external electric power hinder its scalable applications, especially in mobile devices. Herein, we report a bifunctional P, W co-doped Co3N nanowire array electrode with remarkable catalytic activity towards both HzOR (-55 mV at 10 mA cm-2) and hydrogen evolution reaction (HER, -41 mV at 10 mA cm-2). Inspiringly, a record low cell voltage of 28 mV is required to achieve 10 mA cm-2 in two-electrode system. DFT calculations decipher that the doping optimized H* adsorption/desorption and dehydrogenation kinetics could be the underlying mechanism. Importantly, a self-powered H2 production system by integrating a direct hydrazine fuel cell with a hydrazine splitting electrolyzer can achieve a decent rate of 1.25 mmol h-1 at room temperature.

Optical modulation characteristics of zeolitic imidazolate framework-67 (ZIF-67) in the near infrared regime

We report the passively Q-switched (PQS) operation in the near infrared (NIR) regime with as-prepared zeolitic imidazolate framework-67 (ZIF-67) as saturable absorbers (SAs) for the first time, to the best of our knowledge. Based on the excellent saturable absorption properties of the as-prepared ZIF-67, passively Q-switched Nd:GdVO₄ lasers were achieved operating at ⁴F_3/2→²I_11/2 and ⁴F_3/2→²I_13/2 transitions. The stable Q-switched laser's pulses with a pulse width of 120 ns at a repetition rate of 566 kHz and a pulse width of 108 ns at a repetition rate of 415 kHz were obtained, corresponding to the transition ⁴F_3/2→²I_11/2 at 1 µm and the transition ⁴F_3/2→²I_13/2 at 1.3 µm, respectively. The results indicate that the ZIF-67 saturable absorber with the advantages of large modulation depth and high thermal stability is a promising saturable absorber candidate for the NIR pulse generation.