Electrochemistry is a powerful tuning knob for inducing drastic optical property changes. By applying an electrical bias while using counterions to maintain charge neutrality, electrochemistry can vary the carrier density or even trigger a phase transformation in an electrically addressable manner, which is particularly desirable in many applications where tunable range, scalability, or non-volatility is crucial. Meanwhile, metamaterials provide additional degrees of freedom to boost performance and achieve multifunctional control