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Low-cost electrocatalysts with high catalytic activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are essential for electrochemical water splitting to produce hydrogen. In this study, we report the combination of porosification and doping strategy to improve the catalytic activity of NiCo.sub.2O.sub.4-based electrocatalysts for HER and OER. A facile porosification method was proposed and demonstrated by annealing the NiCo.sub.2O.sub.4 nanosheets in a reductive atmosphere to synthesize porous NiCo.sub.2O.sub.4 nanosheets. In order to further improve the catalytic activity for HER and OER, the porous NiCo.sub.2O.sub.4 nanosheets were doped with P and Fe, respectively, which tailored the electronic structure of the electrocatalysts, improved the intrinsic catalytic activity, and increased the number of active sites. HER or OER experiments were performed on the porous P-NiCo.sub.2O.sub.4 nanosheets or the porous NiCo.sub.1.5Fe.sub.0.5O.sub.4 nanosheets, which required an overpotential of 160 mV or 222 mV to deliver a current density of 10 mA/cm.sup.2, respectively. Furthermore, overall water splitting was achieved using the porous P-NiCo.sub.2O.sub.4 nanosheet cathode and the porous NiCo.sub.2-xFe.sub.xO.sub.4 nanosheet anode with a Faraday Efficiency of 98.22%. The present paper proposes a strategy to fabricate doped porous electrocatalysts with a view to providing insights for the design and synthesis of efficient and inexpensive electrocatalysts for water splitting.

Low-cost electrocatalysts with high catalytic activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are essential for electrochemical water splitting to produce hydrogen. In this study, we report the combination of porosification and doping strategy to improve the catalytic activity of NiCo 2 O 4 -based electrocatalysts for HER and OER. A facile porosification method was proposed and demonstrated by annealing the NiCo 2 O 4 nanosheets in a reductive atmosphere to synthesize porous NiCo 2 O 4 nanosheets. In order to further improve the catalytic activity for HER and OER, the porous NiCo 2 O 4 nanosheets were doped with P and Fe, respectively, which tailored the electronic structure of the electrocatalysts, improved the intrinsic catalytic activity, and increased the number of active sites. HER or OER experiments were performed on the porous P-NiCo 2 O 4 nanosheets or the porous NiCo 1.5 Fe 0.5 O 4 nanosheets, which required an overpotential of 160 mV or 222 mV to deliver a current density of 10 mA/cm 2 , respectively. Furthermore, overall water splitting was achieved using the porous P-NiCo 2 O 4 nanosheet cathode and the porous NiCo 2-x Fe x O 4 nanosheet anode with a Faraday Efficiency of 98.22%. The present paper proposes a strategy to fabricate doped porous electrocatalysts with a view to providing insights for the design and synthesis of efficient and inexpensive electrocatalysts for water splitting. Graphical abstract

Cold expansion technology has been widely used in aviation industries as an effective method of improving the fatigue performance of fastener holes. It can improve the fatigue life several times over without adding weight, meeting the growing demand for lightweight and durable aircraft structures. In recent years, it has been extensively studied through extensive experiments and finite element simulations to analyze the residual stresses around the fastener hole. Appropriate process parameters lead to the generation of beneficial residual stresses that influence the material microstructure, thereby improving the fatigue life of the component. This paper summarized factors influencing residual stresses in cold expansion and their effects on fatigue life, and the strengthening mechanism, parameter optimization, and effect of anti-fatigue are discussed from the point of view of the residual stress and microstructure. The development of new cold expansion technologies and the research directions that can realize anti-fatigue technology efficiently are proposed.

Calcareous soil has a strong fixation effect on phosphorus (P), iron (Fe), manganese (Mn), and zinc (Zn), including on the interaction between these elements by limiting their availability and absorption by cotton. Therefore, we propose employing acidic composted tea (CT) to alleviate their contradiction. A pot experiment was set up to explore the CT effect on cotton leaf gas-exchange measurements, availability of P, Fe, Mn, and Zn in calcareous soil, their relationship, and absorption by cotton. The net photosynthetic rate ( Pn ) of fertilization treatments increased by 62.7–65.1% compared with unfertilized control ( p  < 0.05); compared with organic fertilizer application, CT application reduced soil pH by 1%, increased the soil’s Olsen-P by 25.2%, mainly originating from NaOH-P dissolution, and increased the available Fe and Mn by 23.0% and 1.1%, respectively; however, available Zn decreased due to its absorption by cotton. CT also increased trace element accumulation in cotton plants, which significantly affected cotton dry matter and yield. Available soil P increment had no antagonistic effect on trace element availability and accumulation. In contrast, CT promoted P, Fe, Mn, and Zn accumulation in cotton plants, with a synergistic relationship between the absorption of various elements. Fe, Mn, and Zn were constantly removed; hence, they should be supplemented to maintain trace element balance. This study provided new material and methods for managing P and trace elements in calcareous soil.