After following the literature down several different rabbit holes, I found this argument in some of the supplementary figures on that tree that seems to address your question:

> "Supplementary Note 1 | Advantages of PEC hydrocarbon synthesis.

"In general, PEC systems have the potential to combine the performance of wired PV-electrolysis (PV-E) systems with the simplicity of photocatalytic (PC) systems. PV-E is an established technology, which can take advantage of commercial solar cell modules with light harvesting efficiencies above 20% 24 and state-of-the-art gas diffusion electrolysers operating at high current densities above 1 A cm-2.25 However, PV-E assemblies require additional components including reactors, membranes, pumps, corrosive electrolytes, external cables and control electronics, increasing the overall system complexity and associated cost.26,27"

"On the other hand, PC powders provide an inexpensive alternative to PV-E, since light absorber particles and any necessary catalysts are dispersed in solution, which greatly minimises the overall system complexity. However, wide band gaps and charge recombination often limits solar-to-hydrogen conversion efficiencies to below 1%.28 While a homogeneous dispersion of the light absorber and catalyst can increase reactivity, this also poses challenges for the subsequent separation of all components and products from the reaction mixture."

"Accordingly, PEC artificial leaves provide a balance between PV-E and PC approaches in terms of complexity, cost and performance, by integrating state-of-the-art semiconductors and catalysts into a single compact panel. These PEC devices can perform reactions beyond water splitting (e.g., CO2 reduction to C1 products, or the light-driven C2 hydrocarbon and organic synthesis introduced here), while allowing product separation between the anodic and cathodic sides. This intrinsic design advantage is demonstrated by lightweight PEC systems using 15-fold less material than conventional solar panels, which combine the high performance of wired systems with the high activity per gram of photocatalyst nanoparticles.29 This applicability and potential of PEC-based fuel production also translates to hydrocarbon synthesis. In addition, direct light-driven hydrocarbon synthesis is carbon neutral, avoiding the energy-intensive Fischer-Tropsch process for indirect hydrocarbon synthesis from syngas (H2 + CO)."

Practically speaking the catalysts in these processes have relatively short lifetimes, so you'd want to incorporate an efficient catalyst regeneration process into the production pipeline, i.e. you might only get 16-128 hours of efficient production before catalyst regeneration is required so that needs to be built into any commercial process. So if you can design a catalyst that's easy to regenerate, that's very important.

Source material with nice pictures of the copper nanoflowers:

https://static-content.springer.com/esm/art%3A10.1038%2Fs419...