Electrochemical potassium ion intercalation into two-dimensional layered MoS₂ was studied for the first time for potential applications in the anode in potassium-based batteries. X-ray diffraction analysis indicated that an intercalated potassium compound, hexagonal K_0.4MoS₂, formed during the intercalation process. Despite the size of K⁺, MoS₂ was a long-life host for repetitive potassium ion intercalation and de-intercalation with a capacity retention of 97.5% after 200 cycles. The diffusion coefficient of the K⁺ ions in K_xMoS₂ was calculated based on the Randles-Sevcik equation. A higher K⁺ intercalation ratio not only encountered a much slower K⁺ diffusion rate in MoS₂, but also induced MoS₂ reduction. This study shows that metal dichalcogenides are promising potassium anode materials for emerging K-ion, K-O₂, and K-S batteries.

We report a general method to graft aromatic molecules onto graphene thin film electrodes through a simple immersion process. Large-area electroactive graphene thin films grafted with methylene blue (MB) have been developed as electrocatalytic electrodes for the oxidation of β-nicotinamide adenine dinucleotide (NADH). The oxidation of NADH starts from −0.08 V (vs. Ag/AgCl) at the graphene-MB thin film electrodes, showing a decrease of 530 mV in overpotential compared to a Ti metal electrode. The graphene-MB thin films have promising applications in biosensors and biofuel cells due to their ability to promote NADH electron transfer reaction.

High aspect ratio Na_0.44MnO₂ nanowires with a complex one-dimensional (1-D) tunnel structure have been synthesized. We found that the reaction went through layered birnessite nanosheet intermediates, and that their conversion to the final product involved splitting of the nanosheets into nanowires. Based on our observations, a stress-induced splitting mechanism for conversion of birnessite nanosheets to Na_0.44MnO₂ nanowires is proposed. The final and intermediate phases show topotaxy with 〈001〉_f//〈020〉_b or 〈110〉_b where f represents the final Na_0.44MnO₂ phase and b the intermediate birnessite phase. As a result of their high surface areas, the nanowires are efficient catalysts for the oxidation of pinacyanol chloride dye.