Reversible proton ceramic electrochemical cell (R-PCEC) is regarded as the most promising energy conversion device, which can realize efficient mutual conversion of electrical and chemical energy and to solve the problem of large-scale energy storage. However, the development of robust electrodes with high catalytic activity is the main bottleneck for the commercialization of R-PCECs. Here, a novel type of high-entropy perovskite oxide consisting of six equimolar metals in the A-site, Pr1/6La1/6Nd1/6Ba1/6Sr1/6Ca1/6CoO3−δ (PLNBSCC), is reported as a high-performance bifunctional air electrode for R-PCEC. By harnessing the unique functionalities of multiple elements, high-entropy perovskite oxide can be anticipated to accelerate reaction rates in both fuel cell and electrolysis modes. Especially, an R-PCEC utilizing the PLNBSCC air electrode achieves exceptional electrochemical performances, demonstrating a peak power density of 1.21 W cm−2 for the fuel cell, while simultaneously obtaining an astonishing current density of − 1.95 A cm−2 at an electrolysis voltage of 1.3 V and a temperature of 600 °C. The significantly enhanced electrochemical performance and durability of the PLNBSCC air electrode is attributed mainly to the high electrons/ions conductivity, fast hydration reactivity and high configurational entropy. This research explores to a new avenue to develop optimally active and stable air electrodes for R-PCECs.

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Cellulose nanofibers (CNFs) with nanoscale dimension, high aspect ratio, and easily modified surface chemistry show great potential as novel rheological and filtration modifiers in bentonite water-based drilling fluids (BT-WDFs). However, CNFs would suffer from poor redispersibility in an aqueous suspension if they were fully dried for transportation, storage, and field application. Herein, we report a simple, versatile, and scalable strategy to prepare water-redispersible CNFs through compounding them with a water-soluble, commercially available drilling fluid additive, polyanionic cellulose (PAC), and subsequent drying. The results revealed that the water redispersibility of CNF/PAC hybrids was dependent on the PAC's viscosity (i.e., low viscosity, LV; or regular viscosity, R) as well as drying method (i.e., oven drying, OD; or freeze-drying, FD). Among the obtained CNF/PAC hybrids, the CNF/PAC-R material prepared by FD exhibited optimal water redispersibility due to the enhanced suspending capacity of CNF suspension and the minimized capillary force. As a consequence, the CNF/PAC-R hybrids prepared by FD improved the rheological and filtration performance of BT-WDFs more pronouncedly than others, which could lead to better fluid carrying capacity for drilling cuttings and wellbore stability. The PAC acted not only as water-dispersible agents for CNFs but also as additives for modifying the rheological and filtration properties of BT-WDFs. PAC-coated cellulose nanofibers can be used as water-redispersible dry additive for drilling fluids with enhanced fluid performance.

Performance of hardened oil well cement (OWC) is largely determined by the rheological properties of the cement slurries. This work was carried out to investigate the effect of water- to-cement ratio (WCR) and cellulose nanoparticles (CNPs), including cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs), on rheology performance of OWC-based slurries using a Couette rotational viscometer coupled with rheological models. The yield stress and viscosity of neat OWC slurries had a decreasing trend with the increase of WCRs. The suspension became increased unstable with the increase of WCRs. The properties of CNPs, including rheological behaviors, surface properties and morphology, determine the rheological performance of CNP-OWC slurries. In comparison with CNC-OWC slurries, the gel strength, yield stress and viscosity of CNF-OWC slurries were higher as CNFs were more likely to form an entangled network. The gel strength, yield stress and viscosity of CNP-OWC slurries increased with reduced CNF size through regrinding and the proportion of CNFs in the mixture of CNFs and CNCs, respectively.