Water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) enable use of solar energy to carry out fuel-forming reactions. WS-DSPECs are based on catalysts and dyes attached to wide band gap semiconducting metal oxides. Often, these systems operate under harsh conditions so stable surface attachment is a major concern. Anchoring groups have long been used to attach molecular dyes and catalysts to metal oxide surfaces, but often suffer from aqueous instability under the required conditions. Here we optimize the surface loading of the silatrane anchoring group, a triethanolamine protected trialkoxysilane, onto nanostructured titanium dioxide. This anchoring group is not yet widely used because prior protocols afforded low surface coverage, but it has the advantage of high aqueous stability over a wide pH range and at both oxidizing and reducing potentials. A new method for estimating surface coverage was applied here. We find that the loading using previously reported methods is especially low, less than 20% of the loading achieved using a typical carboxylic acid anchor. However, we were able to uncover several factors contributing to this low loading, which allowed us to develop methods to significantly improve surface coverage for various silatranes.  Notably, we were able to increase loading by 145% through use of a benzoic acid additive. Not only does this put silatrane loading on par with other anchors, but it also indicates the level of control that this anchoring group provides. Our results may allow us to exploit silatrane binding properties in the future to design more active, efficient systems through co-loading dyes and catalysts in specified ratios or with controlled surface proximity.

Optimization of surface loading of the silatrane anchoring group on titanium dioxide for use in photoelectrochemical devices

ACS Spring 2022

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