Transition-metal phosphides are of high interest for electrochemical applications, owing to their chemical stability, composition and phase tunability, and economic potential.  
In this talk, I will discuss our new route for metal phosphides synthesis, utilizing a direct reaction of transition-metal nitrate salts with triphenylphosphine (PPh₃) in molten-state. This method was found straightforward, benign and scalable. We demonstrated this method for nanoscale transition-metal phosphides synthesis, as an attractive alternative to common solvothermal or gas-solid phosphidation synthetic methods, allowing tunable phase composition of the produced nanoparticles, along with significant simplification of procedures and equipment.

We initially demonstrated the new method for nickel-phosphides molten-state synthesis from Ni(NO₃)₂^∙6H₂O and triphenylphosphine (PPh₃)[1]. By combining analytical and computational methods, we elucidated the reaction mechanism, indicating that the reaction propagates dominantly through favored Ni-P bonding and consecutive cleavage of phenyl–P bonds of PPh₃. Interestingly, we found both by DFT and XRD that an intermediate formation of metallic nickel nanoparticles, originating from ligand-to-metal charge transfer at the Ni-P bond, is essential for in-situ production of phosphides.

Furthermore, we exemplified the advantages of this simple and controllable method for the investigation of phase/composition-activity correlation of different Ni/P products for hydrogen evolution reaction (HER) and as anode-materials for Li-ion batteries.
We found a clear composition-activity trend for both applications, providing high performance which is comparable to nickel phosphides produced by other common methods. We found Ni₃P products favorable as HER electrocatalysts, with 145 mV overpotential at 10 mA/cm², and Ni₂P was found favorable as LIBs anode materials, with 206 mAh g^-1 capacity; both with high morphological and electrochemical stability.

This new simple synthetic path offers new possibilities for low-cost synthesis and design of other transition-metal based materials. I will present and discuss our latest results of an improved and generalized synthesis method based on the above detailed molten-state method, allowing the production of a variety of single and multi-component transition-metal phosphides for electrochemical applications.