Our objective function (Eq. 1 and Fig ) provided a single metric that incorporated key figures of merit to quantify overall system performance (holistic performance), and was defined as the YieldCO over the QYCO to prioritise a high product yield, as well as the TOFCO of the catalyst and photosensitiser to ensure the system was operating at high efficiency. SelCO is indirectly considered by the YieldCO and TOFCO. w1, w2 and w3 are weighting coefficients to define the relative importance of each metric.