NodeMCU V2 ESP8266 - Use 5VIN as power for heater of a MQ-9 Sensor
The VIN pin is NOT directly connected to the USB's 5V supply as it is an VIN PIN for powering the MCU from an external source other than the USB - this means the pin cannot be used as a 5V supply output.


Never ever connect VIN to a power source AND connect the USB plug. That can destroy the USB port in your computer. There is zero back-powering protection on the MCU board.


According to the datasheet the sensor (heater) needs upto 350mW which IMHO makes powering via an extra power board (which can also power the MCU) a necessity.