review of electrochemical hydrogen sensors based on thermoelectric effects, thermal conductivity, catalytic combustion, surface plasmon resonance, are studied. Understanding the electrochemistry is only the first step in understanding a sensor. After understanding the principles, the sensor's performance must be linked to the operating environment, the device design, and the specific materials and structures used. Electrochemical hydrogen sensors can be divided into three main classes, amperometric, potentiometric, and conductometric sensors. The amperometric gas sensor, or AGS combines versatility, sensitivity, and ease of use in common gas detection situations with a relatively low cost and, recently, with the possibility for miniaturization. Potentiometric sensors are thermodynamic equilibrium sensors for specific electrochemical reactions involving a redox reaction. The measurement of solution resistance is not inherently species-selective in conductometric sensors. The working electrode in an electrochemical sensor is made from a noble metal.