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Photocatalysis – Solar Hydrogen Without Panels & Electrolyzer

Oil companies know that their days are numbered… well, as oil companies. So they are facing the choice of either go extinct or reinvent themselves. That’s actually not too difficult a choice to make.

Take Spanish oil and energy giant Repsol. Where northern Europeans are concentrating on their wind resource, Repsol, situated in one of the sunniest countries in Europe, wants to try its luck with our nearest star. Their strategy: try to avoid using solar panels and electrolyzers and use photons for splitting water directly.

In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a catalyst. In catalysed photolysis, light is absorbed by an adsorbed substrate. In photogenerated catalysis, the photocatalytic activity (PCA) depends on the ability of the catalyst to create electron–hole pairs, which generate free radicals (e.g. hydroxyl radicals: •OH) able to undergo secondary reactions. Its practical application was made possible by the discovery of water electrolysis by means of titanium dioxide (TiO2).

The principle has been known since 1911, discovered by a German scientist Alexander Eibner, when he studied pigments.

However, a breakthrough in photocatalysis research occurred in 1972, when Akira Fujishima and Kenichi Honda discovered electrochemical photolysis of water occurring between connected TiO2 and platinum electrodes, in which ultraviolet light was absorbed by the former electrode, and electrons would flow from the TiO2 electrode (anode; site of oxidation reaction) to the platinum electrode (cathode; site of reduction reaction); with hydrogen production occurring at the cathode. This was one of the first instances in which hydrogen production could come from a clean and cost-effective source.

Repsol is planning to build a 100 kilo/day H2 photocatalytic demo-reactor in Puertollano, Spain and hopes to own a commercially attractive method of producing hydrogen this way by 2030, together with gas grid operator Enagas. Envisioned start date: 2024. By 2028, production should be scaled-up towards 10 tonnes/day. Both companies have secured EU funding for the project.

[] – Repsol and Enagás will develop technology to produce renewable hydrogen
[] – Repsol-Enagas Renewable H2 Project Gets EC’s Financial Backing
[] – Repsol, Enagas secure EU funds for photoelectrocatalytic hydrogen production
[] – ‘Very disruptive’ direct solar-to-hydrogen commercially viable by 2030, says oil group Repsol
[] – Photocatalysis
[] – Photocatalytic water splitting
[] – Repsol
[] – Enagás

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Elektrolyse: Sauberer Wasserstoff für die Zukunft

Popularized German language video about electrolyser technology.

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