Solar Optofluidics (SOLO): Water Splitting beyond the 1.23 eV Thermodynamic Constraints

Lead Research Organisation: Loughborough University
Department Name: Chemical Engineering


Renewable hydrogen will play an important role in the UK's energy future for low carbon transport, heating, grid-scale energy storage and CO2 capture/utilisation. The UK's hydrogen demand would reach 143~860 TWh/year by 2050, while the current production capacity is only 27 TWh/year. Conversion of abundant sunlight to produce H2 is one of attractive approach to meet the demand. Among various solar H2 technology, photoelectrochemical (PEC) water splitting has gained much attention due to its operational flexibility, reduced electron-hole recombination and natural separation of H2 and O2 in two electrodes.

Learning from the historic trajectory of solar PV commercialisation, the key to deliver market acceptable PEC hydrogen production will be (1) enabling the use of much cheaper materials (such as silicon) and (2) significantly increasing the STF efficiency to at least 20%.

SOLO aims to remove the 1.23 eV thermodynamic restraints from the PEC water splitting system, by developing a pH-differential strategy to alter the individual equilibrium potentials of anodic (OER) and cathodic (HER) half reactions, thus reducing the energy barrier. A novel membraneless optofluidic platform is proposed to accommodate the pH-differential design, where acid and alkaline electrolyte will be able to co-exist in a single cell. Promising low bandgap materials will be demonstrated in the SOLO platform to achieve cost effectiveness and high STF efficiency.

Planned Impact

This project will conduct transformative research on a novel pH-differential optofluidics engineering platform, SOLO, to reduce the cost and enhance the energy efficiency of solar fuel production from photoelectrochemical (PEC) water splitting. It is believed to boost international and inter-sectoral knowledge transfer with diverse interests, thereby benefit the industrial advancement and economy growth of UK and beyond, particularly solar energy, hydrogen and energy materials.

The UK has growing needs for alternative energy vectors such as hydrogen to support its low-carbon economy and there is significant potential to develop solar fuel technology for H2 production to meet this demand. This project will deliver technological innovation on eco-attractive solar hydrogen production to support the UK's transition to a low carbon future, and consequently, increase the robustness of the UK economy. The project outcomes will contribute to achieving the UK's ambitious and legislated targets of 100 % renewable energy and 80 % carbon emission reduction by 2050. The SOLO platform developed in this project are critical to meet the UK energy and environmental demands, as well as ensuring security of supply.

The government-led Technology Innovation Needs Assessment (TINA) 2014 revealed that the creation of a UK hydrogen industry has the potential to contribute £19-50 billion to the economy by 2050. The barrier to apply solar hydrogen production in the UK is its high cost (currently $10/kg, compared to $3-4/kg from wind and biomass). The SOLO project aims to develop an enabling technology, i.e., pH-differential optofluidic platform, to remove the 1.23 eV thermodynamic constraints from current PEC water splitting systems, allowing (1) an increase in the solar-to-fuel (STF) efficiency and (2) the use of low bandgap inexpensive materials for PEC devices, which are known as the two most important factors to drive down the solar H2 costs. Increasing the STF efficiency from 5% to 20% could cut 2/3 of PEC H2 production costs, while reducing the cell cost has the potential to half the H2 production costs (Energy Environ Sci, 2013, 6, 1983). If the above targets can be met, as to be addressed in the proposed work, the H2 production costs can reach the U.S. Department of Energy's targeted threshold of $2-4/kg H2. This project offers the chance to make PEC water splitting a viable route for H2 production.


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Kalamaras E (2018) Solar carbon fuel via photoelectrochemistry in Catalysis Today

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Tsang C (2020) Graphene materials in green energy applications: Recent development and future perspective in Renewable and Sustainable Energy Reviews

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EP/R012164/1 01/01/2018 31/05/2018 £101,118
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Description We have developed a novel microfluidic photoelectrochemical reactor Utilising to produce sustainable fuels from water and CO2, in which sunlight is used to convert the greenhouse gas (CO2) into a usable form of stored chemical energy. We found that the microfluidic design could enhance the solar-to-fuel efficiency by an order of magnitude compared with traditional batch type reactors
Exploitation Route The findings are published in academic journal papers. We are also invited an oral presentation in the Faraday Discussion Artificial Photosynthesis in Cambridge. It is expected that the finding will first impact a wide research community via high impact publications and invited talks.
Sectors Energy

Description Enagagement workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact A project start-up meeting and engagement workshop were held, for which around 10 participants attended. The project direction and industrial engagement strategies were discussed and made clear.
Year(s) Of Engagement Activity 2018
Description Press release 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact A press release and media interview were held regarding the SOLO project by BBC. The news has been widely highlighted in various medias (such as Times) and significantly increase the impact of the project.
Year(s) Of Engagement Activity 2018
Description The Future of Renewable Energy & Fuels Workshop: Academia-Industry Dialogue 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Renewable energy and fuels play a crucial role in the UK's energy future for low carbon transport, heating, electricity and industrial processes. Supported by EPSRC, several research projects are currently underway in the organisers' groups to look into technological innovations towards high-performance and low-cost renewable (bio-, solar- or e-) fuel production and energy storage.

Stakeholder engagement, especially industrial engagement, is vital as it provides the foundation to share knowledge and increase linkages between different sectors to increase the momentum in renewable energy. In particular, this allows us, at an early stage of technological development, to gain a better understanding and to predict the key barriers to commercialization, other development drivers, policy support and regulations in addition to commercialization and scale-up potentials.

To this aim, we are organising a workshop to open academia-industry dialogue on renewable fuel generation and energy storage. The workshop comprises of keynote talks and panel discussions on the topics of renewable biofuels, solar fuels, e-fuels and energy storage; their associated science and engineering fundamentals such as material development, reactor design, new in-situ characterisation techniques and modelling and simulation; as well as the entrepreneurial aspects such as techno-economics, market uptake, public acceptance and policies and regulations.

Around 50 participants from industrial and academic sectors attended the workshop.
Year(s) Of Engagement Activity 2019