The reaction of Fe(N(SiMe(3))(2))(3) with PH(3) in THF at 100 °C gives amorphous FeP(2) in high yield. As an anode material in a Li ion battery, this material shows remarkable performance toward electrochemical lithiation/delithation, with gravimetric discharge and charge capacities of 1258 and 766 mA h g(-1), respectively, translating to 61% reversibility on the first cycle and a discharge capacity of 906 mA h g(-1) after 10 cycles. This translates to 66% retention of the theoretical full conversion capacity of FeP(2) (1365 mA h g(-1)).

We present the first alkaline redox flow battery (a-RFB) based on the coordination chemistry of cobalt with 1-[Bis(2-hydroxyethyl)amino]-2-propanol (mTEA) and iron with triethanolamine (TEA) in 5 M NaOH. The overall redox system has a cell voltage of 0.93 V in the charged state. Importantly, the coordination compounds are negatively charged and have limited transport through the cation exchange membrane (e.g., Nafion), minimizing the extent of redox species crossover during charge-discharge cycling. Fe-TEA is electrochemically reversible and soluble up to 0.8 M, whereas Co-mTEA presents quasireversible electron transfer kinetics and can be solubilized up to 0.7 M. Cyclability was tested with a flow cell at a concentration 0.5 M up to 30 cycles using a 50 μm thick Nafion membrane, at 30 mA/cm 2 , with minimal crossover (less than 4% of net concentration) or evolution of gases detected. The redox flow battery (RFB) has excellent potential for electrical grid energy storage. However, it has not yet been widely deployed often because of problems of stability and limited cycle life. In this report we describe the use of coordination compounds of cobalt with 1-[Bis(2-hydroxyethyl)amino]-2-propanol (mTEA, Figure 1A), and iron with triethanolamine (TEA, Figure 1B) in 5 M NaOH as a RFB. The flow battery was optimized to achieve stable cycling with 71% average energy efficiency in 30 cycles when passing 30 mA cm −2 , and using a 50 μm-thick Nafion membrane as the separator, at a concentration 0.5 M. Importantly, crossover of the redox species through the membrane was below 5% of the original concentration at the end of the 30 th cycle, with no evolution of gases detected during cycling. We developed this alkaline RFB as an alternative to state of the art RFBs, e.g., the all vanadium RFB, which are based on acidic electrolytes.1 Acidic RFBs often suffer capacity fading due to membrane crossover and the occurrence of undesired secondary reactions during battery cycling (e.g., precipitation, evolution of H 2 and Cl 2 gases).2 Acidic electrolytes have a high conductance, G max = 825 mS cm −1 for 3 M H 2 SO 4(aq), 3 but tend to be corrosive to the cell components, which translates into high operational and maintenance costs. 4 In contrast, alkaline electrolytes such as NaOH have lower conductance, G max = 410 mS cm −1 for 3.7 M NaOH (aq) 3 , but are less corrosive. Alkaline electrolytes employing transition metals generally require the use of coordination compounds as redox species to prevent precipitation of the hydroxides or hydrous oxides. The net charge on these ions can be tailored by ligand selection to minimize membrane crossover with a cation exchange membrane. Moreover, different ligands can be used to tune the electrode potential of the half-cells to optimize the voltage of the battery. 5The formation of chemically stable soluble coordination compounds of cobalt and iron in 5 M NaOH is challenging because of a thermodynamic tendency to form their insoluble hydroxides. For iron(III), with a solubility product, K sp , ...

A stable hydrophobic ionic crystalline solid comprised of the N-propyl-N-methylpiperidinium cation and hexafluorophosphate anion PP13PF6 exhibits a remarkably wide electrochemical window of 7.2 V.

The air stable tetra-phosphine complexes trans-MCl(2)(PH(3))(4) (M = Ru, Os) are formed in high yield from reactions of MCl(3).3H(2)O with PH(3) in MeOH.