Vanadium redox flow batteries suffer from inefficiencies partly due to the kinetics of the V²⁺/V³⁺ reaction, for which lack of mechanistic understanding hinders electrolyte and electrocatalyst design to improve reaction rates. Here, we provide insights into the V²⁺/V³⁺ reaction in HClO₄, H₂SO₄, HCl, HBr, and HI. We identify the V²⁺ and V³⁺ structures in these electrolytes using extended X-ray absorption fine structure, UV-vis, and density functional theory; this includes the hydrated structures of V²⁺ and V³⁺ in water (i.e., without anion complexation). We show that V²⁺/V³⁺ kinetics correlate with the energy of vanadium intermediate bound to carbon through a bridging anion (∗[bridge−V³⁺]). The anion-induced kinetic enhancement is from a decreased activation energy because of changing ∗[bridge−V³⁺] energy. The ∗[bridge−V³⁺] energy increases in the order of anion polarizability (OH⁻ < Cl⁻ < Br⁻ < I⁻), explaining previous reports that correlate anion polarizability with the kinetics of other 3d transition metal ion redox couples.

钒氧化还原液流电池效率低下的部分原因在于V ²⁺ / V ³⁺反应的动力学，对此缺乏机械理解会阻碍电解质和电催化剂设计以提高反应速率。在这里，我们提供了有关HClO ₄，H ₂ SO ₄，HCl，HBr和HI中的V ²⁺ / V ³⁺反应的见解。我们使用扩展的X射线吸收精细结构，UV-vis和密度泛函理论确定了这些电解质中的V ²⁺和V ³⁺结构。这包括V ²⁺和V ³⁺的水合结构在水中（即没有阴离子络合）。我们表明，V ²⁺ / V ³⁺动力学与通过桥联阴离子（* [bridge-V ³⁺ ]）结合到碳上的钒中间体的能量相关。阴离子引起的动力学增强是由于改变* [bridge-V ³⁺ ]能量而使活化能降低。的* [桥-V ³⁺ ]在阴离子极化的顺序能量增大（OH ^-  <氯^-  <溴^-  <I - ^），说明以往的报告其归属关系阴离子极化与其他3动力学d过渡金属离子的氧化还原对。