When vegetable waste (VW) is used as a sole substrate for anaerobic digestion (AD), the rapid accumulation of volatile fatty acids (VFAs) can impede interspecies electron transfer (IET), resulting in a relatively low biogas production rate. In this study, Chinese cabbage and cabbage were selected as the VW substrates, and four continuous stirred tank reactors (CSTRs) were employed. Different concentrations of biochar-loaded nano-Fe₃O₄(Fe₃O₄@BC) (100 mg/L, 200 mg/L, 300 mg/L) were added, and the organic loading rate (OLR) was gradually increased during the AD process. The changes in biogas production rate, VFAs, and microbial community structure in the fermentation tanks were analyzed to identify the optimal dosage of Fe₃O₄@BC and the maximum OLR. The results indicated that at the maximum OLR of 3.715 g (VS)/L·d, the addition of 200 mg/L of Fe₃O₄@BC most effectively promoted an increase in the biogas production rate and reduced the accumulation of VFAs compared to the other treatments. Under these conditions, the biogas production rate reached 0.658 L/g (VS). Furthermore, the addition of Fe₃O₄@BC enhanced both the diversity and abundance of bacteria and archaea. At the genus level, the abundance of Christensenellaceae_R-7_group, Sphaerochaeta, and the archaeal genus Thermovirga was notably increased.

The practical application of potassium metal batteries (PMBs) has been hindered by serious dendrite growth and volume variation on the potassium (K) metal anode. Altering the deposition behavior of K metal by designing a three-dimensional (3D) scaffold is an ideal strategy to inhibit the dendrite growth and volume variation. Here, a self-standing and gradient-potassiophilic 3D porous scaffold composed of Ti₃CN on the separator side and Ti₃CN and SnF₂ nanoparticles on the anode side (named 3D-T/TSF) is designed to modify the K metal anode, achieving excellent electrochemical performance. The potassiophilicity of the 3D-T/TSF scaffold increases in gradient along the direction perpendicular to the electrode, which induces the preferential deposition of K metal within the 3D-T/TSF scaffold. Such deposition behavior could fully occupy the internal pore structure of the scaffold, inhibiting the K dendrite growth and relieving the volume variation. In addition, an inorganic SEI layer rich in K–Sn alloy, SnO₂, and KF is spontaneously formed at the interface between the anode and electrolyte to enhance the stability of the K anode. Consequently, the 3D-T/TSF@K//3D-T/TSF@K symmetric battery presents a long cycle lifespan of over 1200 h at 0.5 mA cm⁻². The 3D-T/TSF@K//PTCDA full battery delivers a capacity retention of 88.5% after 100 cycles at 1C. The design of the gradient-potassiophilic 3D porous scaffold provides a new direction for the construction of stable K metal anodes, which is beneficial for promoting the practical application of PMBs.