System and methods for detecting a composition in a wellbore during a cementing operation. An electrochemical cell can be disposed towards an end of a wellbore. The electrochemical cell can generate electrical energy in response to a physical presence of a composition at the electrochemical cell. The composition can be pumped from a surface of the wellbore during a cementing operation of the wellbore. Further, a telemetry signal indicating the physical presence of the composition at the electrochemical cell can be generated based on the electrical energy generated by the electrochemical cell. As follows, the telemetry signal can be transmitted to the surface of the wellbore.