A critical new research direction in solid oxide cells (SOCs) is related to balancing power-grid load or integrating heat-electricity-gas interconnection simply by switching operations between the fuel-cell and electrolyser mode. The rational design of robust and high-performance materials for SOCs is urgent for high conversion/energy efficiencies. Iron is highly abundant and offers suitable and flexible redox chemistry for the two operation modes. Iron-based oxide materials are widely investigated for SOCs because of their low cost and, more importantly, the appropriate valence stability of the Fe–O bond for excellent redox activity across a wide range of electrode functions. This review describes the progress in iron-based materials for SOCs, especially the recent applications in electrode materials or catalysts. The stable structure of the ferrite oxides provides an important platform for improved performance via the substitution of Fe in the fuel electrodes of an SOC with H₂/H₂O or carbonaceous fuel/feedstock. Furthermore, we discuss nano-sized Fe⁰ metal or alloys on an oxide electrode via infiltration and in situ exsolution aiming to fabricate highly active electrocatalysts. The advances of ferrite oxide-based oxygen electrodes are also discussed in terms of thermal expansion, stability and electrocatalysis before the developments of symmetrical and reversible SOCs based on ferrite oxides are classified and summarized. Therefore, the challenges and future prospects are discussed.

Violet phosphorene, a recently produced elemental 2D material, is a promising electronic and optoelectronic structure. The work function and band alignment of phosphorene nanoflakes are essential for their heterojunction structure design. The work function of violet phosphorene nanoflakes has been shown to decrease with the increase in layers from 5.16 eV to 4.79 eV and tends to be stable on a gold substrate, which has been confirmed via Kelvin probe force microscopy. The work functions measured on a silicon oxide substrate are much higher due to charge accumulation. The experimental work function of few-layer violet phosphorene is different from the intrinsic work function due to substrate doping, while that of thick violet phosphorene nanoflakes approaches the intrinsic work function value. Various functionals have been adopted for the work function calculation of few-layer violet phosphorene and the values obtained have been compared to the experimental results. The band alignments of different layered violet phosphorene materials calculated using the most accurate functional are demonstrated and compared to those of well-known materials to give a practical route for future applications. The work functions of the violet phosphorene nanoflakes have been shown to decrease due to oxidation, but they significantly improve after annealing in an argon atmosphere.