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Renewable fuel generation is essential for a low carbon footprint economy. Thus, over the last five decades, a significant effort has been dedicated towards increasing the performance of solar fuels generating devices. Specifically, the solar to hydrogen efficiency of photoelectrochemical cells has progressed steadily towards its fundamental limit, and the faradaic efficiency towards valuable products in CO2 reduction systems has increased dramatically. However, there are still numerous scientific and engineering challenges that must be overcame in order to turn solar fuels into a viable technology. At the electrode and device level, the conversion efficiency, stability and products selectivity must be increased significantly. Meanwhile, these performance metrics must be maintained when scaling up devices and systems while maintaining an acceptable cost and carbon footprint. This roadmap surveys different aspects of this endeavor: system benchmarking, device scaling, various approaches for photoelectrodes design, materials discovery, and catalysis. Each of the sections in the roadmap focuses on a single topic, discussing the state of the art, the key challenges and advancements required to meet them. The roadmap can be used as a guide for researchers and funding agencies highlighting the most pressing needs of the field.

Quantitative description of electrolyte impact is established for nanoscale water electrolysis prevalent during photocatalytic overall water splitting.

Photocatalytic water splitting using semiconductor particulates is an effective technique for solar-energy conversion to chemical energy in the form of hydrogen molecules. The photocatalytic reactions proceed via two half reactions: the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). The active sites in these reactions are electrocatalysts that have been deposited on particulate photocatalyst surfaces. It is important to understand the electrocatalyst potential during the photocatalytic reactions to understand the reaction mechanism. Several measuring methods have been developed for photoelectrodes, but it is still challenging to measure the electrocatalyst potential directly during unbiased overall water splitting with particulate photocatalysts. This study presents an inverted photocatalyst structure to evaluate the operating potential of CoOOH electrocatalysts during overall water splitting. The structure consists of Al-doped SrTiO3 (SrTiO3:Al) photocatalyst powder deposited on a CoOOH electrode. In addition, we estimated the fraction of holes that reach the SrTiO3:Al photocatalyst surface after carrier generation in the bulk from the light-intensity dependence of the CoOOH electrocatalyst potential balanced with the hole quasi-Fermi level in the photocatalyst. The hydrogen production rate was found to be controlled by modulating the potential applied to the CoOOH electrode, which perturbs the hole quasi-Fermi level in the SrTiO3:Al photocatalyst. [ABSTRACT FROM AUTHOR]

This study investigated the ammonia decomposition mechanism over Ru/CeO2. Isotopic tests using ND3 revealed that the rate-determining step involves adsorbed nitrogen atoms on Ru. Moreover, an inverse kinetic isotope effect where ND3 decomposition was faster than NH3 was clearly observed. The origin of the inverse effect was explained by the lower D coverage on the catalyst surface compared to H coverage for mitigating the inhibition of ND3 activation. [ABSTRACT FROM AUTHOR]

Microwave‐driven catalytic processes have attracted the attention of many researchers and industries as these processes are powerful strategies for use in industrial electrification. However, undetectable hot spots inside the catalyst bed can be misleading in terms of the deceptive effects of microwaves on acceleration of catalytic reactions because of the lack of physicochemical knowledge about these processes. In this paper, the hot spots temperatures were estimated based on catalytic ammonia (NH3) synthesis/decomposition equilibrium. The reaction temperature estimated from the chemical equilibrium was more than 100 °C higher than the catalyst bed surface temperature measured with an infrared thermometer under microwave irradiation. Assuming a formation of very steep local high temperature fields, rigorous kinetic analysis led to an estimate that the active site fraction which reaches the high temperature was only about 10 % of total sites. Compared with a resistivity heating furnace, the energy input was reduced by more than 85 % under microwave irradiation. The temperature estimated by the chemical equilibrium was almost corresponding to the temperature estimated by an oscillation of extended X‐ray absorption fine structure recorded under microwave irradiation. This paper presents a proposal for a method to estimate hot spots based on thermodynamic equilibrium, yielding a quantitative evaluation of energy consumption reduction caused by microwaves. [ABSTRACT FROM AUTHOR]

Achieving a highly stable and selective oxygen evolution reaction (OER) in the presence of chloride ions (Cl−) is imperative for the future practical application of seawater splitting technology. This approach can streamline complex purification processes and avoid competition with the demand for drinking water. In this report, we present novel electrolyte engineering through mixed buffers – specifically, the utilization of borate/phosphate at a non-extreme pH of 9.2 – to achieve stable OER. Our findings demonstrate that borate serves as the primary buffer, maintaining localized pH stability, while the addition of phosphate acts as the main stabilizer for the Ni component. Electrochemical analysis and ex situ/operando spectroscopic characterization reveal that phosphate selectively forms a stabilized Ni complex. This complex effectively suppresses the corrosion and dissolution of Ni, resulting in an extended operational lifetime without compromising OER performance, even in the presence of Cl−. Furthermore, electrochemical measurements conducted with various redox probes indicate the formation of a passive Ni layer which leads to improved stability rather than the charge repulsion effect proposed in an alkaline pH environment. This study underscores the significant potential arising from the simultaneous advancement of both electrocatalysts and electrolytes. [ABSTRACT FROM AUTHOR]