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December 25, 2023

Harnessing Sunlight to Drive Sustainable CO2 Conversion

As the world attempts to move towards carbon neutrality, the NTT Group, which itself is aiming to achieve carbon neutrality by 2040, is leading a number of promising initiatives that include the generation of renewable energy and enhancing energy efficiency.

NTT is also pioneering research in artificial photosynthesis, a technology that has the potential to exceed the carbon dioxide (CO2) conversion performance of natural photosynthesis.

Artificial photosynthesis, which uses inorganic materials including semiconductors and catalysts, is a promising solution for converting and immobilizing atmospheric CO2 into carbon monoxide (CO) and formic acid (HCOOH). It not only addresses the issue of existing emissions, but also provides a sustainable pathway for future emission management. However, until now its development has faced challenges, primarily in maintaining continuous CO2 conversion over extended periods. Most existing technologies have only managed several hours to tens of hours of operation, with degradation control being a significant hurdle.

NTT's research offers a potential leap over this hurdle, with a new artificial photosynthesis process involving an oxidation electrode made from a semiconductor photocatalyst and a reduction electrode composed of a metal catalyst. A key challenge has been designing electrodes that are corrosion-resistant and durable enough for long-term reactions. NTT's laboratory prototype device addresses this by integrating a long-life semiconductor photocatalyst electrode, using light as energy, with a fibrous metal catalyst electrode to efficiently convert CO2.

Initial results are very promising: NTT has set a new global benchmark by facilitating the world's longest continuous carbon fixation under simulated sunlight for 350 hours, which surpasses the annual carbon absorption rate of a regular Cryptomeria japonica (Japanese cedar) tree. In doing so, it converted a cumulative 420g/m2 of carbon, showcasing a significant step forward in CO2 reduction using renewable energy. The potential of this technology in mitigating climate change and fostering a sustainable society is huge.

NTT's success in enabling artificial photosynthesis hinges on two key technological improvements that make the process more efficient and long-lasting.

1. Protecting the key component: The first major advancement is in protecting the semiconductor photocatalyst, a crucial component that uses light for energy. NTT's prototype devices adds a very thin layer of nickel oxide to this component. The layer, only 2 nanometers thick (in other words, two billionths of a meter), acts like a shield. It smooths out any rough spots and allows light to pass through easily, which helps prevent the component from wearing out quickly.

2. Efficiently converting CO2 from gas: The second advancement involves how CO2 is converted. Traditional methods have focused on CO2 dissolved in water; however, there were limitations due to the low amount of CO2 that water can hold and the possibility of unwanted chemical reactions. NTT redesigned the electrode to work directly with CO2 gas instead of dissolved CO2. The new design integrates a special fibrous metal that allows CO2 gas to spread through it easily and an electrolyte membrane that provides the necessary protons to cause the chemical reaction. This setup significantly improves the efficiency of CO2 conversion, making it over ten times more effective than previous methods.

As it looks to the future, NTT aims to further boost the efficiency and lifespan of its semiconductor photocatalyst electrodes. The technology is poised not only for further laboratory testing, but also for outdoor application, where it will be used to manage CO2 emissions and do its part to combat climate change.

By harnessing the power of sunlight and its innovation know-how, NTT is paving the way towards a world where environmental sustainability and technological advancement go hand in hand.

NTT--Innovating the Future of Sustainability

Picture: Daniel O'Connor

Daniel O'Connor joined the NTT Group in 1999 when he began work as the Public Relations Manager of NTT Europe. While in London, he liaised with the local press, created the company's intranet site, wrote technical copy for industry magazines and managed exhibition stands from initial design to finished displays. 

Later seconded to the headquarters of NTT Communications in Tokyo, he contributed to the company's first-ever winning of global telecoms awards and the digitalisation of internal company information exchange. 

Since 2015 Daniel has created content for the Group's Global Leadership Institute, the One NTT Network and is currently working with NTT R&D teams to grow public understanding of the cutting-edge research undertaken by the NTT Group.