Heterogeneous photocatalytic CO2 reduction has attracted significant attention as a promising route for solar fuel and chemical production [1, 2]. Among the possible reaction pathways, gas-phase CO2 hydrogenation remains comparatively underexplored despite its potential to produce methanol (CO2 + 3 H2 -> CH3OH + H2O) and other valuable chemicals under mild conditions [3]. By avoiding the energetically-demanding water oxidation half-reaction, CO2 hydrogenation represents a unique opportunity for single-bandgap photocatalysis by relaxing the requirement of a large photovoltage which then significantly limits the fraction of solar spectrum absorbed [4]. CO2 photo-hydrogenation therefore offers an alternative carbon utilization technology to energy-intensive thermocatalysis that can be coupled with renewable hydrogen generation and carbon capture to realize a more sustainable future.

Despite its potential, significant challenges continue to hinder progress. Photocatalytic activities remain low due to challenges in simultaneously achieving suitable optoelectronic properties, catalytic performance and material stability [1, 3]. Equally important, but often overlooked, are the experimental challenges associated with photocatalytic CO2 reduction [1]. Low product formation rates necessitate highly sensitive analytical methods and rigorous experimental protocols, while variations in reactor configurations, light sources, and the lack of standardised testing procedures hinder reproducibility. Together, these factors increase the risk of experimental artefacts complicating the reliable evaluation and comparison of photocatalyst performance between different laboratories.

This presentation identifies the common pitfalls encountered during photocatalytic CO2 hydrogenation and examines experimental factors that influence the measured performance. Firstly, the effect of reactor configuration, light source used, operating conditions and sample deposition methodology on the final photocatalytic performance is quantified. The challenge of standardization demonstrated and the distinction between surface area normalized and apparent photocatalytic activity is highlighted [5]. We next examine the erroneous sources of products species with particular attention on contamination, photocatalyst decomposition, and degradation of reactor/system components (such as polymer seals and recirculating pump materials). Based on empirical evidence, guidelines for good photocatalysis experimental design are outlined and the our photocatalytic experimental setup is presented. Furthermore, to address the issue of contamination-free gas recirculation, we present a novel custom-made hermetically-sealed piston pump designed to meet the challenging requirements of high-pressure contamination-free gas recirculation in batch experiments. The open-source design provides a low-cost and reproducible platform for the community. Finally, we consider the role of control experiments in establishing product origin demonstrating how the source of artefacts can be identified through systematic control experiments.

By identifying common sources of experimental error and outlining practical recommendations for reactor design, analytical protocols, and validation strategies, this work aims to support more robust, reproducible, and comparable photocatalytic CO2 hydrogenation research.