Sustainable Oxidation Catalysts for the Production of Solar Hydrogen and Chlorine from Brine

Summary

The primary aim of this project is to produce new, sustainable oxidation catalysts that allow the creation of efficient wireless, photodiode, solar to chemical energy conversion devices for the splitting of brine/seawater. In brine, H2, alkali and Cl2 (or H2 and sodium hypochlorite, NaOCl will be the (separated) products. Hydrogen will be stored to provide heat at a later date (by burning) or used to produce electricity (via an H2/O2 fuel cell).

The oxidised chloride will be stored either as Cl2, or hypochlorite, to provide a route to chlorinate water, or provide a disinfectant. The programme will produce inexpensive demonstrators which can be readily scaled up for use in the household - i.e. on a 'personalised' energy and disinfectant scale. Such systems are particularly suited for use in the developing countries, although the subsequent development of substantially scaled up systems - involving solar farms - will allow the production of these valuable, storable, chemical products at a level suitable for widespread use by a town and/or local industry. The latter scaled up systems will form the basis of a subsequent, second follow on stage, industry led, developmental program of work, whereas the first stage project described here will focus on the proof of concept and initial creation of scalable demonstrators.

The proposed novel ClOCs developed in the project will utilise inexpensive, abundant nanomaterials (such as: oxides of Mn, Ni or Co), although, in some cases, these will be doped with well-dispersed, much more active, but less abundant ones, such as Ru dioxide. These nanomaterials will also be coated onto high surface area conducting carbons, which will allow them to be partly supported and active. A novel, combinatorial approach, using High-throughput Continuous Hydrothermal flow synthesis, HiTCH and, to a lesser extent, other - electrochemical and photochemical synthetic methods, will be used to produce a wide range of oxidation catalysts. Novel, colour-based rapid screening methods will be used to provide initial assessments of their activities and a wide range of techniques will be used to assess their physical properties.

The best of the catalysts generated will be optimised in terms of performance as electrocatalysts and subjected to more detailed electro-kinetic and structural studies (e.g. XANES and XAFS) and subsequent mechanistic and structural modelling. This work will help identify key structural features associated with the most active of the electrocatalysts tested and inform on the best routes to be taken in the subsequent synthesis of related materials as oxidation catalysts of possible greater potential. Finally, the best of all the electrocatalysts tested will be used to create simple, exemplar, scalable working wireless photodiode solar energy conversion devices, which utilise inexpensive, efficient, triple-junction Si photovoltaic cells as the light-absorbing unit, for the photocleavage of water or brine (including seawater).

Impact summary
The major project impact areas include:

(i) Society; by developing science & technology to improve the quality of life and by aiding policy makers and legislators of national and international agreements on carbon dioxide reduction. The solar to chemical energy and disinfectant conversion devices for local use developed in this programme have the capability of transforming energy production and sanitary levels (re: clean surfaces and potable water) in all developing nations and so improve the quality of life of over a billion people;

(ii) the Economy; through the design, production and commercialisation of new classes of inexpensive, effective catalysts for the electro-oxidation of water or brine, in partnership with one or more leading UK industries, such as Johnson Matthey, PV3 and Amalyst. Similarly, working with large scale industry such as Akzo Nobel, will lead to the development of sustainable, revenue-generating routes for the production of hydrogen and chlorine via inexpensive, commercially viable photodiodes for both personal (i.e. local) and future large-scale use;

(iii) Knowledge; as significant advances in oxidation catalysts and nanoscience will be delivered, methodologies for rapid production and screening will be developed and knowhow created regarding the design and construction of scalable demonstrators of the technology;

(iv) People; through the technical expertise developed by the research team during the project, the training received in societal and ethical issues and the transferable skills developed in engagement with the media, the general public, policy makers and legislators.

In addition to the obvious benefits to academic researchers in the field (summarised on the EPSRC form), the main beneficiaries include:
(a) Society: The potentially disastrous effects, to the environment and so to Society, of climate change due elevated levels of CO2 in the atmosphere arising from fossil fuel burning will be reduced through the creation of an efficient, inexpensive, long-lasting solar to chemical energy conversion device for brine splitting. The ability for such a system to produce chlorine products for disinfecting surfaces or producing potable water at the domestic (and eventually industrial scales) will benefit all peoples by providing low cost sustainable cleaning agents and clean water, particularly in developing countries.

(b) Commercial sector: Numerous industries will benefit from the development and harnessing of the novel catalysts for the cleavage of brine into H2 and oxidised chloride (i.e. Cl2 or hypochlorite). The former has the added advantage (over O2) of providing a source of chlorinated water and/or disinfectant. The novel, 'personal' energy and disinfectant generating devices delivered in this project will be robust and inexpensive (so no large capital outlay), as they largely comprise earth-abundant materials (as catalysts and semiconductor) operated under ambient conditions and driven by freely available solar light, rather than grid electricity as in commercial industrial electrolysis. Industrial beneficiaries will include: renewable energy producers, water companies and producers of domestic cleaning products.

(c) Government/public sector: The work will directly impact globally that of policy makers and legislators with regard to future carbon dioxide production minimisation goals. The provision of safe and clean drinking water is also of relevance to government/the public sector globally.

(d) More speculative beneficiaries of this research are charities and voluntary organisations, since, by being able to produce clean drinking water or disinfectants in areas hit by disasters which have no electricity supply, it will be able prevent or reduce suffering by readily allowing provision of chlorinated water or cleaning agents, and hydrogen fuel.