3D Printing as an Adaptive Tool for Sensor Fabrication Applied through pH Monitoring
Franc Paré, Mingyue Pan, Oscar Guerrero‐Sodric, Juan Antonio Baeza +2
AI summary
72% confidenceThis paper develops 3D-printed iridium oxide (IrOx) pH sensors integrated into a modular platform for monitoring ammonia recovery in a bioelectrochemical reactor. The sensors achieve super-Nernstian response (−77 ± 0.2 mV/pH), high reproducibility (RSD < 5%), and stability for ≥20 days. The platform enables multi-point pH profiling in the recovery chamber where H⁺ and NH₄⁺ are converted to H₂ and NH₃ via gas-diffusion cathode, with recovered NH₃ acidified back to NH₄⁺ salts. The work demonstrates that 3D printing enables custom sensor geometries and integration with reactor-specific components, addressing a gap in electrochemical sensing tools for ammonia recovery systems.
Key insights
Performance IrOx electrodes of different lengths (64–118 mm) maintain consistent sensitivity (79–80.1 mV/pH) despite 1.4% variation, proving that 3D-printed device electrical resistance does not limit pH sensor performance across the design range.
So what. Designers can use longer electrodes for spatial profiling in the recovery chamber without recalibrating or sacrificing sensitivity, enabling asymmetry mapping of cathode performance.
Threshold Sensor sensitivity decreases 9–12% over 20 days, but the rate of decay halves after day 5, stabilizing sufficiently for 15+ day operation and week-long experiments with minimal replacement.
So what. Operators can plan sensor replacement intervals around 15 days for continuous monitoring without frequent maintenance, but should expect initial drift in the first week.
Performance 3D-printed Ag/AgCl reference electrode shows only 2.9 ± 0.3% difference in sensitivity compared to commercial reference despite 225 ± 2 mV potential shift, confirming interchangeability and reversibility.
So what. Fully 3D-printed sensor platforms can replace commercial reference electrodes without recalibration, enabling true miniaturization and integration into custom reactor geometries.
Trade-off Electrode width must be increased to 1.2 mm to prevent contact with reactor cathode and mechanical failure under plate pressure, revealing a critical design constraint for integration.
So what. When integrating 3D-printed sensors into plate reactors, account for mechanical tolerance and electrical isolation by increasing non-conductive shell width; test fit before full assembly.
Mechanism pH response time varies inversely with pH extremity: <15 s at pH < 5 and pH > 10, but 50–120 s in the neutral range (5 < pH < 10), indicating slower kinetics in buffered regions.
So what. For real-time monitoring of ammonia recovery (where pH rises from ~1 toward neutral as acid is consumed), expect slower sensor response in the critical mid-range; use averaging or predictive algorithms.
Opportunity areas6
Specific gaps in this paper, with an experiment that would close each.
High No data on pH sensor performance in the presence of dissolved ammonia (NH₃) or ammonium (NH₄⁺) at the concentrations expected in the recovery chamber (likely > 0.1 M after acid neutralization). Interference from these species on IrOx response is not characterized.
Section 2.4 states the recovery chamber is filled with 1.0 M H₂SO₄ and ammonia is generated and diffuses into it, but all calibrations (Figures 3–7) were performed in phosphate buffer or pure acid/base titrations without NH₃/NH₄⁺ present. The paper does not report whether high ammonium concentration affects sensor sensitivity or response time.
Try. Calibrate sensors in 1.0 M H₂SO₄ spiked with 0.1–1.0 M NH₄⁺ or NH₃ and compare sensitivity and response time to calibrations in buffer alone; measure potential drift over 24 h in static high-ammonium solution.
High No measurement of actual pH evolution or ammonia recovery rate during bioelectrochemical reactor operation. The paper states sensors were 'placed in the recovery chamber' and 'tracked the operativity of the biological reactor by indirectly measuring the amount of ammonium recovered' but provides no time-series data, recovery efficiency, or correlation between pH rise and NH₄⁺ accumulation.
Section 2.4 ends abruptly: 'With such a sensor distribution, a clearer picture of the asymmetry of the cathode can be studied... Moreover, they tracked the operativity of the biological reactor by indirectly measuring the amount of ammonium recovered. The recovery chamber is filled with 1.0 M H₂SO₄...' and then the text is cut off ('cou'). No results from reactor operation are presented.
Try. Run a complete bioelectrochemical ammonia recovery cycle with the 3D-printed sensor platform; record pH at 5 different heights/positions over 24–72 h; measure final NH₄⁺ concentration by ion chromatography or titration; correlate pH rise rate to current density and cathode potential.
High No investigation of sensor performance under the electrochemical conditions of the bioelectrochemical reactor (applied cathode potential, current density, presence of biofilm). All characterization was done at open-circuit potential (OCP) in abiotic solutions.
Section 2.1 states 'Measurements were performed under continuous stirring and in OCP conditions so a Nernstian response can be observed.' The reactor operates under applied potential (cathode for ammonia generation), which may cause electrochemical noise, fouling, or potential interference with the sensor's reference electrode.
Try. Calibrate and measure pH response of 3D-printed sensors in a three-electrode cell with applied cathode potential (−0.5 to −1.0 V vs Ag/AgCl) and current density (10–100 mA/cm²) typical of ammonia recovery; assess potential drift and noise; test in presence of biofilm or bacterial culture.
Medium No data on sensor performance in the presence of sulfate (SO₄²⁻) at 1.0 M concentration (from H₂SO₄ in recovery chamber). Potential interference from high ionic strength or specific anion adsorption on IrOx is not addressed.
Section 2.4 specifies 'The recovery chamber is filled with 1.0 M H₂SO₄' but all calibrations used phosphate buffer (1 mM) or dilute acid/base. High sulfate concentration may affect electrode surface chemistry, double-layer capacitance, or proton activity coefficient.
Try. Calibrate sensors in 1.0 M H₂SO₄ (matching reactor conditions) and compare sensitivity and response time to calibrations in phosphate buffer; measure potential drift in static 1.0 M H₂SO₄ over 7 days.
Medium No characterization of sensor behavior at pH < 2 or pH > 12, despite the paper mentioning that conventional glass electrodes have poor accuracy at pH < 1 and strong Na⁺ interference at pH > 12. The operating range of the 3D-printed sensors in extreme conditions is not defined.
Figure 3A shows calibration from pH ~2 to pH ~12, but the paper does not explicitly state the validated operating range or discuss performance at the extremes. The recovery chamber starts at pH ~0 (1.0 M H₂SO₄) and rises as ammonia is absorbed; the lower bound is critical but untested.
Try. Calibrate sensors in 1.0 M H₂SO₄ (pH ~0) up to pH 2, and separately in pH 11–13 solutions; report sensitivity, response time, and hysteresis at each extreme; define the validated operating range.
Low No comparison of 3D-printed sensor cost, fabrication time, or material consumption versus commercial pH electrodes. The economic and practical advantages of the 3D-printing approach are not quantified.
The paper emphasizes that 'conventional glass-type pH meters... suffer from drawbacks such as high fabrication cost, difficulty of miniaturization, glass-electrode brittleness' and that 'there is a significant lack of research into pH sensors dedicated to this field,' but does not provide cost or time data for the 3D-printed alternative.
Try. Document material cost (PLA filament, IrOx precursor, Ag ink, PVB membrane), fabrication time (printing, activation, electrodeposition, assembly), and labor per sensor; compare to commercial electrode cost and lead time; calculate cost per sensor and cost per measurement over 20-day lifetime.
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Abstract
As a key parameter, pH has received a lot of attention from the sensing perspective. New materials and technologies are being used to produce state of the art devices capable of tracking it. However, most generic sensors lack the applicability that certain applications require. In this article, 3D printing technology is used to its full potential to produce electrodes, which are modified into pH sensors and reference electrodes, with shapre‐driven additional functionality for monitoring ammonia recovery in a bioreactor. The 3D‐printed electrodes are modified with a layer of iridium oxide to be turned into pH sensitive devices. Their characterization showed their characteristic super‐Nernstian response (−77 ± 0.2 mV pH −1 ), high reproducibility (RSD < 5%) between sensors and repeatability (RSD < 2%) between measurements. Moreover, the sensors are stable for at least 20 days and tunable in length. All of this results in the sensors being built into a functional shape and tested to monitor the performance of an ammonia‐producing bioelectrochemical reactor.
Keywords
Identifiers
- Journal
- ChemElectroChem
- Year
- 2025
No 3D model is mapped to this paper yet. Parameter ranges above still place reported values on the literature distribution.