Photoelectrochemical water-splitting efficiency hits 4.5%

January 16, 2020

Photoelectrochemical (PEC) water splitting for hydrogen fuel generation has been considered the Holy Grail of electrochemistry. But to achieve it, many scientists believe the materials have to be abundant and low cost.

The most promising oxide photocathodes are cuprous oxide (Cu2O) photoelectrodes. In 2018 and 2019, researchers at EPFL achieved champion performance with cuprous oxide, rivaling photovoltaic (PV) semiconductor-based photocathodes.

But there was still a piece missing from the puzzle. Even state-of-the-art Cu2O photocathodes still use metallic back contacts (copper or gold), allowing for considerable electron-hole recombination. Other disadvantages include high cost and that the metal contact won't allow unabsorbed sunlight to pass through.

Now, scientists at EPFL show for the first time, that copper thiocyanate (CuSCN) can be used as a transparent and effective hole transport layer (HTL) for Cu2O photocathodes with overall enhanced performance. The research was led by Professors Anders Hagfeldt, Michael Grätzel, and Kevin Sivula at EPFL's Institute of Chemical Sciences and Engineering.

Detailed analysis on two types of CuSCN showed that a defective structure could be beneficial for hole conduction. Moreover, due to the coincidental alignment between valence bands of CuSCN and Cu2O, the band-tail states assisted hole transport in CuSCN was discovered to allow smooth hole conduction while efficiently block electron transport.

The optical advantages of CuSCN were further exhibited through a standalone PEC-PV tandem delivering a solar-to-hydrogen efficiency of 4.55%. This efficiency (4.55% for 12 h) is currently the highest among all Cu2O-based dual-absorber tandems.

The study presents a clear and impressive advancement beyond the state-of-the-art Cu2O photocathodes, which can contribute and inspire future development in the field.

"Though top numbers are achieved with the oxide material in this work, we believe higher values are not far," says Pan Lingfeng, the paper's first author. "At least three aspects are found to be not optimal, but improving them is very feasible. The efficiency value is getting closer and closer to the one that was previously thought to be the threshold for commercialization."

Linfeng Pan, Yuhang Liu, Liang Yao, Dan Ren, Kevin Sivula, Michael Graetzel, Anders Hagfeldt. Cu2O photocathodes with Band-tail States Assisited Hole Transport for Standalone Solar Water Splitting. Nature Communications 16 January 2020. DOI: 10.1038/s41467-019-13987-5

Ecole Polytechnique Fédérale de Lausanne

Related Copper Articles from Brightsurf:

New material 'mines' copper from toxic wastewater
A team of scientists led by Berkeley Lab has designed a new material -- called ZIOS (zinc imidazole salicylaldoxime) -- that targets and traps copper ions from wastewater with unprecedented precision and speed.

Team uses copper to image Alzheimer's aggregates in the brain
A proof-of-concept study conducted in a mouse model of Alzheimer's disease offers new evidence that copper isotopes can be used to detect the amyloid-beta protein deposits that form in the brains of people living with -- or at risk of developing -- Alzheimer's.

Copper boosts pig growth, and now we know why
Pigs have better feed conversion rates with copper in their diets, but until now, scientists didn't fully understand why.

Cancer cells spread using a copper-binding protein
Researchers at Chalmers University of Technology, Sweden, have shown that the Atox1 protein, found in breast cancer cells, participates in the process by which cancer cells metastasise.

Adding copper strengthens 3D-printed titanium
Successful trials of titanium-copper alloys for 3D printing could kickstart a new range of high-performance alloys for medical device, defence and aerospace applications.

Matrix could ensure vital copper supplies
Researchers have identified a matrix of risks that the mining industry must overcome to unlock vitally important copper reserves.

Do microbes control the formation of giant copper deposits?
One of the major issues when studying ore deposits formed in surficial or near-surface environments is the relationship between ore-forming processes and bacteria.

Copper compound as promising quantum computing unit
Chemists at Friedrich Schiller University in Jena (Germany) have now synthesised a molecule that can perform the function of a computing unit in a quantum computer.

Copper ions flow like liquid through crystalline structures
Materials scientists have sussed out the physical phenomenon underlying the promising electrical properties of a class of materials called superionic crystals through the investigation of CuCrSe2.

A copper bullet for tuberculosis
Tuberculosis is a sneaky disease, and the number one cause of death from infectious disease worldwide.

Read More: Copper News and Copper Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to