Single-layer fuel cells (SLFCs) based on mixed semiconductors and ionic conductors demonstrate  simplified material preparation and fabrication procedure and possess high performance potentially. However, the operational stability and principle of SLFCs have not yet been convinced of either commercialization or fundamental interests. We hereby report on the employment of a perovskite oxide-based phase-structured redox-stable semiconductor prior to determining a possible solution that improves the durability of the SLFC. Feasible working principles are established and an in-depth understanding of the short-circuit-free phenomenon in SLFCs with the mixed ionic and electronic conductors is provided. Additionally, a smart material design and cell structure processing are also proposed. An extended nonstop testing period of up to 2 days confirms the project feasibility and improved durability of the SLFCs, achieved by replacing the unstable lithiated oxide phase with redox-stable perovskite oxide, though the electrochemical performance is sacrificed. The precipitated metal/alloy nanoparticle on perovskite oxide not only improves the electrode reaction kinetics but also facilitates the charge separation and ionic conduction in SLFCs, consequently enhancing the fuel cell performance and electrical efficiency. The results confirmed the potential of stable operation for future practical deployment of SLFCs via appropriate selection of material and cell structure design. It is greatly believed that the physical junction plays a crucial role in overcoming the internal short-circuit issue of SLFCs.

The reversible solid oxide cell (RSOC) is an attractive technology to mutually convert power and chemicals at elevated temperatures. However, its development has been hindered mainly due to the absence of a highly active and durable fuel electrode. Here, we report a phase-transformed CoFe-Sr 3 Fe 1.25 Mo 0.75 O 7−δ (CoFe-SFM) fuel electrode consisting of CoFe nanoparticles and Ruddlesden-Popper-layered Sr 3 Fe 1.25 Mo 0.75 O 7−δ (SFM) from a Sr 2 Fe 7/6 Mo 0.5 Co 1/3 O 6−δ (SFMCo) perovskite oxide after annealing in hydrogen and apply it to reversible CO/CO 2 conversion in RSOC. The CoFe-SFM fuel electrode shows improved catalytic activity by accelerating oxygen diffusion and surface kinetics towards the CO/CO 2 conversion as demonstrated by the distribution of relaxation time (DRT) study and equivalent circuit model fitting analysis. Furthermore, an electrolyte-supported single cell is evaluated in the 2:1 CO-CO 2 atmosphere at 800°C, which shows a peak power density of 259 mW cm −2 for CO oxidation and a current density of −0.453 A cm −2 at 1.3 V for CO 2 reduction, which correspond to 3.079 and 3.155 mL min −1 cm −2 for the CO and CO 2 conversion rates, respectively. More importantly, the reversible conversion is successfully demonstrated over 20 cyclic electrolysis and fuel cell switching test modes at 1.3 and 0.6 V. This work provides a useful guideline for designing a fuel electrode through a surface/interface exsolution process for RSOC towards efficient CO-CO 2 reversible conversion.

The formation of nitrogen-containing compounds in bio-oil during microwave pyrolysis of Chlorella and Spirulina microalgae has been investigated in this study. Activated carbon (AC) and magnetite (FeO) were used as microwave receptors during microwave pyrolysis experiments. It has been found that the use of FeO increased the total yield of bio-oil. The use of different microwave receptors did not seem to have affected the total yield of nitrogen-containing compounds in the bio-oil. However, FeO promoted the formation of nitrogen-containing aliphatics, thereby reducing the formation of nitrogen-containing aromatics. The use of AC promoted the dehydration reactions during amino acid decomposition, thereby enhancing the formation of nitrogen-containing aromatics during pyrolysis. From the gas chromatography-mass spectrometry (GC-MS) analysis results, the major high-value nitrogen-containing compounds in the pyrolysis bio-oil of Chlorella and Spirulina were identified as indole and dodecamide. The formation mechanisms of nitrogen-containing compounds were proposed and discussed.

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