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Development of efficient catalysts for oxygen evolution reaction (OER) remains challenging in PEM dehumidifier or vapor electrolyzer. This study developed novel coaxial IrOx@SbSnOxnanofiber (NF) catalysts by electrospinning using a dual-channel needle. This method ensures the fibrous structure and the uniform loading of Ir oxide on the support of antimony tin oxide (ATO). IrO2@SbSnOxnanoparticles were synthesized for comparison. Characterizations showed that the active area and charge transfer resistance of NF was 1.47 times and 17.72% of that of commercial ones, respectively. The overpotential of NF at 10 mA·cm–2was 359 mV, much smaller than that of commercial IrO2(418 mV). In addition, the reaction overpotential of NF increased by only 38 mV after 1000 cyclic voltammetry cycles, indicating good electrochemical stability. To explore the enhancement mechanism, first-principles calculations were conducted for theoretically simulating the hetero-structures. Based on d-band theory, the structure formed between ATO and IrO2can effectively weaken the adsorption of oxygen intermediates on the catalyst surface, which reduces the OER energy barrier from 1.705 to 1.632 eV, causing an over 15% decrease of overpotential after loading on ATO. As a practical attempt, we applied the new catalysts in real PEM assembly for air dehumidification and found that the performance was improved by about 2 times compared with that using commercial catalysts. This study provides a research direction for the design of one-dimensional NF catalysts and their using in PEM applications.

•A heat and mass transfer model for heat pipe with composite wick is developed.•Heat transfer is predicted by introducing effective liquid friction coefficient.•The effect of mesh coverage area in the hybrid wick structure is investigated.•The hybrid wick structure can reduce the UTHP thermal resistance up to 48.9%.

Humidity gradient-based power generators (HGPGs), which can convert moisture potential into electric power, offer a promising avenue due to the wide and abundant distribution of air humidity in surrounding environment. Considering the air relative humidity is between 100% and 60% at 25 °C, the enthalpy difference, 3.94 kJ·kg−1, is noteworthy. HGPGs show broad application prospects in distributed power supply and self-powered electronics such as humidity sensors and human respiration monitoring. In this review, recent research on HGPGs since 2015 with the humidity gradient along in-plane and in-thickness direction was summarized. In-plane HGPGs have the advantage of long-term stable power generation (> 150 h), while in-thickness HGPGs can realize the higher current density (> 550 μA·cm−2). However, existing HGPGs are still less efficient, less than 5% of the ideal value. Feasible enhancement methods were summarized, including structural modification through connection design and multi-component assembly, and material modification through doping of high-valent metal cations and introducing of oxygen-containing functional groups. In particular, the addition of hydrogel in HGPG assembly can provide a stable humidity gradient under various environmental conditions, while the performance is significantly affected by the type and amount of hydrogel. Furthermore, mechanism research of energy conversion is far from reaching a consensus. The current theoretical analyses focused on the necessary formation conditions of ion pairs, the separation reasons of positive and negative ions and the influencing factors of their directional movements. Molecular dynamics simulations such as Ab initiomethod allow the visualization of microscopic conversion processes, which are considered a suitable method for illustrating how HGPGs work in the future. This review will serve interested readers as a shortcut and reference for understanding the development process, and stimulate further discussion on fundamentals and optimizations of humidity-based power generators.