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The “year” in this story was not a year outdoors: a research photoelectrochemical (PEC) cell ran continuously for more than 2,200 hours, a duration the 2014 report framed as equivalent to one year of outdoor operation. The result showed a promising way to limit corrosion while splitting water, but it did not establish a consumer hydrogen generator or a commercially ready system.
What the 2014 water-splitting result means
In a report published on 21 November 2014, Chemistry World described a US team led by Nathan Lewis at Caltech operating a PEC cell continuously for over 2,200 hours. The report called that duration the equivalent of one year of outdoor operation. It was a time equivalence, not a claim that the device ran outside for a calendar year.
A PEC device uses light-absorbing semiconductor electrodes in an electrochemical cell to drive water splitting, producing hydrogen and oxygen. The result concerned a research device, not a packaged hydrogen generator intended for household use. Chemistry World reported 100% Faradaic efficiency for oxygen evolution, meaning the measured charge was fully accounted for in producing oxygen in the reported reaction. That figure is specific to oxygen evolution; it is not a solar-to-hydrogen efficiency or a measure of how much sunlight became stored chemical energy.
The report cited the underlying paper by M. R. Shaner and colleagues in Energy & Environmental Science (2015), DOI 10.1039/c4ee03012e. Chemistry World’s coverage does not provide enough protocol detail to establish the experiment’s illumination, electrolyte, pressure, temperature, or electrode geometry, so those conditions should not be inferred from the duration alone.
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How the design addressed photocorrosion
Photocorrosion occurs when a semiconductor electrode degrades in the electrolyte instead of sustaining the intended water-splitting reaction. In a PEC cell, that creates a direct conflict: the electrode must contact the electrolyte and transfer charge, yet that same environment can damage it.
Silicon microwires lowered effective current density
The team used arrays of silicon microwires to increase the electrochemically active area relative to the electrode’s surface area. Spreading reaction over more active sites lowers the effective current density at the electrode–electrolyte interface, helping reduce the conditions that drive corrosion.
Rank #2
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A conductive barrier protected the semiconductor
A protective coating acted as a corrosion-resistant barrier while still allowing charge transfer. A barrier that blocked the electrochemical reaction would defeat the purpose, so the reported strategy had to protect the silicon without electrically isolating it from the reaction.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsA catalyst supported oxygen evolution
An oxygen-evolution catalyst promoted water oxidation. Together, the microwire structure, conductive protective coating, and catalyst addressed different parts of the same stability problem: distribute the interfacial reaction, shield the semiconductor, and facilitate the desired chemistry.
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What the reported operating time does—and does not—prove
The duration was notable because it demonstrated continuous operation for more than 2,200 hours with no noticeable corrosion reported in the 2014 coverage. It did not, by itself, establish the device’s long-term efficiency, output at commercial scale, maintenance interval, or ability to withstand a full range of outdoor weather and operating conditions.
In the same report, photoelectrochemist Brian Seger of the Technical University of Denmark said: “The fact that the Lewis group could test their device for three months with no noticeable corrosion indicates that this hurdle is surmountable.” Materials scientist Dongyuan Zhao of Fudan University described the work as a breakthrough and said it “shows great potential for industrial application.” Those are expert assessments of the result, not evidence that the cell was industrially ready.
Rank #4
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- [USER-FRIENDLY]: Easy to use, it helps enthusiasts understand hydrogen and oxygen generation through water electrolysis, verifying the composition of water
- [VERSATILE EDUCATION]: Ideal for school education, this kit enhances hands-on skills, fosters observation, and analytical abilities among students
How later scale-up demonstrations compare
Later examples in a 2025 review involve immobilized photocatalyst systems, not the Lewis group’s PEC electrode architecture. In these systems, photocatalyst powder is fixed as a thin layer on a substrate. Immobilization can avoid continuously dispersing powder and can make catalyst recovery or replacement easier. Some designs use one photocatalyst for overall water splitting; two-step Z-scheme systems use separate photocatalysts for hydrogen and oxygen evolution, with charge transfer linking the reactions.
| System reported in the 2025 review | Architecture and area | Duration and reported performance | Important qualification |
|---|---|---|---|
| Overall-water-splitting demonstration | Photocatalytic system; 1 m² | About 0.4% solar-to-hydrogen (STH) efficiency under natural sunlight | The review reports the area, natural sunlight and approximate efficiency; it does not establish a comparable operating duration in the summarized information. |
| SrTiO₃:Al system | Immobilized photocatalyst; 100 m² and 1,600 reactor units | Operated for over a year; peak STH conversion efficiency of 0.76% under optimized conditions | The peak is not representative annual output. The review reports regular photocatalyst-sheet replacement, describes it as cumbersome, and identifies low efficiency and negative energy balance among the challenges. |
| Sm₂Ti₂O₅S₂/CNT/BiVO₄ device | A separate immobilized photocatalyst device; area not stated in the review summary | 270 hours without noticeable attenuation under the conditions summarized by the review | This is a different design from the 2014 silicon-microwire PEC cell. |
These figures come from the 2025 review of immobilized photocatalyst devices, not from a direct head-to-head test. They show progress in device area and operating duration, but the figures cannot be ranked fairly without accounting for architecture, illumination, operating conditions, and maintenance.
Best Value
- Core Demonstration: This water electrolysis experiment device is designed to demonstrate water electrolysis and oxygen production in a clear, hands-on way, making it a practical teaching instrument for home school, classroom, and laboratory use
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How to read water-splitting efficiency claims
Solar-to-hydrogen (STH) efficiency compares the chemical energy stored in hydrogen with the incident solar energy. Apparent quantum efficiency (AQE) instead compares photons used in the reaction with incident photons at a specified wavelength. They measure different things and are not interchangeable; neither can be substituted for the 2014 report’s Faradaic-efficiency figure.
A useful comparison also needs the system type and illuminated area, light source, operating pressure and temperature when reported, duration and degradation, and whether the efficiency is a peak or sustained result. Gas separation and safety, maintenance needs, energy balance, and cost matter when judging whether a laboratory or demonstration system can become a practical installation. The 2025 review’s account of sheet replacement and negative energy balance illustrates why a large area or long run time alone does not demonstrate commercial readiness.
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