Methods and apparatus for measuring hydrogen sulfide in downhole fluids

A method of determining a concentration of hydrogen sulfide in a liquid within a wellbore, the method comprising:

• operably coupling, to at least a component of a downhole component, a sensor comprising a pair of electrodes and a sensing material electrically coupled to each electrode of the pair of electrodes, major surfaces of the electrodes of the pair of electrodes opposing each other by a gap within which the sensing material is located;
• advancing the downhole component to a downhole location within a wellbore;
• applying, to the sensor, a voltage of less than about 500 millivolts at a frequency greater than about 10 kHz;
• measuring an electrical resistance across the sensing material responsive to exposure of the sensing material to a liquid within the wellbore;
• and
• determining a concentration of hydrogen sulfide in the liquid based on measured electrical resistance.