pH Sensitivity Estimation in Potentiometric Metal Oxide pH Sensors Using the Principle of Invariance

Table 3

Summary of C₁ capacitance variation model results.

MOx	Electrolyte	Annealing method	Ns (sites/nm^2)	εs	pHpzc	C1 × 10^–6 (F/cm^2)	Calculated absolute pH sensitivity (mV/pH)	Experimental absolute pH sensitivity (mV/pH)	% difference between calculated and experimental results
RuO2	KCl	High temp. (unhydrated)	12.6	55.2	5.526	0.0140	59.1082	57.0 [11]	3.699
		High temp. (unhydrated)	17.6	55.2	5.527	0.0197	59.1094	60.69 [10]	2.604
Ta2O5	KCl	High temp.	4	50	3.922	298.53	34.6144	35.3 [12]	1.942
		High temp.	6	50	3.930	423.93	36.5067	-	-
		Low temp.	10	25	4.594	0.00686	59.1081	59.0 [9]	0.183
		Low temp.	12	25	4.594	0.0124	59.1075	59.0 [9]	0.182
TiO2	KCl	High temp.	2.7	80	5.294	322.46	30.0011	30.0 [8]	0.004
		High temp.	5	80	5.283	518.7	33.9604	-
		High temp.	7	35	5.618	728.21	35.5242	37.73 [65]	5.846
		Low temp.	12.5	35	5.733	0.0175	59.105	58.21 [64]	1.538
Al2O3	KCl	Low temp.	12.04	10.43	8.645	0.0247	59.105	—	—
		High temp.	1.3	10.43	8.777	130.83	29.6951	—	—