Preparation of a cobalt–Fe2+-based phosphate sensor using an annealing process and its electrochemical performance

•The annealing process is introduced into the development of a phosphate sensor.•The sensor has a large detection range and a low detection limit.•The sensor is convenient for mass-scale production.•It is easy to integrate the sensor into handheld equipment. A novel method of detecting dihydrogenphosphate (H2PO4-) in aqueous solutions by electrodepositing a cobalt–iron alloy on a chip was proposed. The sensor showed a linear response to dihydrogenphosphate (H2PO4-) in the concentration range from 1×10-6M to 1×10-2M at pH 4.0 with a slope of -26.69mV/dec, giving a detection limit of 3.41×10-5M. The original chip was then annealed for 70 s at 400 °C to produce an improved version of the sensor with a linear range from 1×10-6M to 1×10-1M at pH 4.0 and a slope of -20.803mV/dec. The detection limit was 2.14×10-6M. The proposed sensor had a good, rapid response and was stable for at least 16 days. The sensor was also unaffected by the anions and cations commonly present in aquaculture water, such as NO3-, NH4+, and SO42-.