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. 2026 Jan 29;2(2):67–76. doi: 10.1021/aps.5c00034

A Multifaceted Vision of Challenges and Opportunities in Practical Artificial Photosynthesis Devices

Siglinda Perathoner 1, Can Li 2,*, Jijie Wang 2, Rengui Li 2, Wangyin Wang 2, Gabriele Centi 1,*, Valentino Romano 3
PMCID: PMC13034413  PMID: 41919053

Abstract

The landscape and status of artificial photosynthesis devices for solar fuels are analyzed by critically combining indications from roadmaps and status reports, patent and literature trends, a market perspective analysis, and an examination of selected ongoing projects in the field. This multifaceted approach aims to provide an innovative vision of opportunities and accelerate their implementation. It integrates insights from multiple perspectives to overcome the partial view of priorities and key elements needed to foster development in the area. Additionally, they include strategies to accelerate implementation from individual analyses. This is recognized as a crucial current gap. Recommendations are provided for aspects that should be introduced to accelerate progress toward significant implementation before 2050, based on this analysis and methodological approach.

Keywords: solar fuels, artificial photosynthesis, artificial leaf, solar devices, solar fuel scenario

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1. Introduction

The ongoing energy transition, based on renewable (solar) energy, is associated with a systemic societal revolution marked by technologies that go beyond the use of fossil fuels and enable distributed, resilient production using local resources and energy, minimizing externalities. − Artificial photosynthesis devices (APDs) are a key enabler of this sustainable vision, playing a crucial role in clean fuel production, carbon circularity, and the transition to a fully renewable economy with energy independence. There is growing research interest in APDs, with many reviews summarizing various scientific aspects. Only a few are cited here; − more are reported in the Supporting Information (SI). As an example of this growing interest, the number of reviews containing the keyword “solar fuel” rose from two in 2004 to 19 in 2014 and to 672 in 2024 (Scopus source).

The concept we use here to define APDs is that of devices that use solar light directly and only to drive the conversion of small molecules (such as CO2 and N2) into more complex and functional chemicals. The IUPAC definition of artificial photosynthesis refers to the photocatalytic production of substances from simple compounds using light adsorbed by chromophoric systems mimicking the action of antennae and reaction centers in natural photosynthetic organisms. This definition does not make the distinction between uphill and downhill photocatalysis, e.g., between photosynthetic and photocatalytic processes. This relevant distinction was instead earlier made by Nozik and Bard as commented by Osterloh.

These devices should progressively integrate other functionalities to mimic those present in natural leaves or trees, such as the capability of (i) capturing feed directly from the environment and (ii) converting these small molecules to complex ones, including carbohydrates, lipids, and proteins, or directly usable chemicals such as fertilizers. These devices should be independent of a supply or electrical grid and avoid further downstream conversion. Biohybrid systems to enable these complex transformations are an emerging direction. This definition of APDs is more restrictive than that used in the literature and does not include, for example, the production of H2 alone (solar H2).

We focus our discussion here on device aspects rather than artificial photosynthesis (AP) itself. We believe they are a crucial factor in accelerating the energy transition, providing a key technology for converting solar energy into molecules for energy and chemical uses, i.e., solar fuels and chemicals (SFCs). The development of APDs requires an axiomatic design that balances component requirements in terms of functionality (e.g., light absorption, catalysis, and ion transport) with system engineering and societal and technoeconomic constraints. Thus, bottom-up (scientific) aspects are combined with top-down elements in a system engineering framework. Several companies and funding agencies are looking to invest heavily in research and development in the area. Still, a limiting factor is the need to identify better challenges and opportunities in APDs and SFCs. Such an objective requires going beyond the conventional scientific reviews and analyzing from a multifaceted approach the trends, challenges, opportunities, and constraints in practical APDs, which is the scope of this perspective. In fact, perceptions of status, prospects, and gaps are often misleading when based solely on the literature’s results.

We aim to overcome the limitations that arise from restricted (specific) viewpoints by adopting a multifaceted approach that critically analyzes roadmaps and status reports, patent and literature trends, market perspective analyses, and research projects. However, it is not intended to make a systematic review of the literature. The aim is to provide food for thought rather than certainties because the complexity and still-evolving APD landscape make it premature to offer conclusive indications. The results are also analyzed in light of the findings from a Horizon Scanning Workshop on Solar Fuels and Chemicals, organized in March 2023 by JRC/EIC. ,

2. A Starting Discussion Point: The EIC Horizon Prize on Artificial Photosynthesis

Given the cited complexity and uncertainties in comparing emerging APDs solely based on literature indications, a platform to compare them directly is recommended but is not yet available. At this stage, the only direct comparison, for at least a part of them, was given by the EIC Horizon Prize “Fuel from the Sun: Artificial Photosynthesis”. This 5M€ award, open to applications from the world scientific community, aimed to select the best APDs using sunlight, water, and “carbon from the air” (e.g., CO2) to produce sustainable fuels. The prize promotes demonstration-scale solutions. Of the 22 applications submitted, three teams were selected as finalists and invited to demonstrate their solutions during a 3-day test run. The SI provides additional indications for these chosen examples.

A first comment is in regard to the validity of the indications from this prize. While further developments have occurred later and only a part of the possible demonstration-scale solutions have been submitted, the relevance of this prize has stimulated participation of top technologies. The main result is that, for the first time, a direct comparison of proposed technologies has been made, thereby identifying limits (particularly in stability; only the winning technology lasted for 3 days) that do not clearly emerge from the literature. The winning prototype system splits water into hydrogen and oxygen using photocatalyst particles. The purified hydrogen and carbon dioxide are then converted into methane. ,

Reliability and stability were considered the main selection criteria rather than performance alone or solar-to-fuel (STF) efficiency, which was less than 1% in the winning technology. While the literature focuses mainly on the latter aspects, even with some attention to scalability and durability, , S&T practice prevailed in the prize decision over performance. On the other hand, stability is a critical factor that is often underestimated but crucial for applications.

STF may be improved in particulate photocatalysis (the winning technology), , through different strategies, such as extending the light absorption range (e.g., with a dual-band absorber), separating the functions, or combining photocatalytic and photothermal effects. Still, the STF is up to 1 order of magnitude lower than in physical separation of redox reactions, such as in photoelectrocatalytic (PEC) and related approaches, mainly when the conversion of CO2 or N2 rather than H2O is addressed. An example is a PV-driven electrocatalytic cell (based solely on earth-abundant components) that enables STF >10% for CO2 conversion and high current densities. The lesson is the need for an axiomatic design, as commented before. It suggests that, even if challenging, direct STF conversion is required and that the steps of the complex machinery (as in natural photosynthesis) should be functionally separated, but in an integrated rather than a cascade approach.

Today, however, a multistep process is the only feasible one at a demonstration stage. An example is the “Liquid Sunshine” project, in which an electrochemical water splitting unit driven by a PV park is coupled to a semi-industrial-scale thermocatalytic CO2-to-methanol unit (1000 tons/year). A hundred-times scaled-up industrial plant has been under construction in Erdos, China, since 2024. This process has a solar energy conversion efficiency of over 17%, which is much higher than that of natural photosynthesis in plants. Note that many prototype/demo-scale plants are under development but are typically limited to solar H2 production. One of the largest is the “Hydrogen farm” project in China. As indicated in the introduction, we do not consider these cases as examples of APDs. Many prototype units are also under development in the framework of research projects (for example, REFINE, SUNGATE, and other EU projects). What is often missing in many of these approaches, even when they are called AP, is an effective analysis of whether the entire process is endergonic (including feed and downstream processing), as in natural photosynthesis.

Interfacing artificial photosynthesis of SFCs with synthetic biology is another emerging direction in technology integration. For example, multicascade enzymatic processes for starch synthesis from CO2 may be accelerated by feeding solar methanol. The hybrid process converting CO2 to starch shows an energy efficiency 3.5 times higher than starch synthesis in maize. The next step is to downsize the approach to realize cost-effective, artificial-tree-like technologies. Another example recently reported by Li et al. demonstrates that l-lactic acid (LA) with optical purity can be synthesized using the same principle.

3. Gaps and Impact Indications from Roadmaps and Technological Status Reports

3.1. A Study on Solar Fuel Research and Investments

A relevant study on SFCs was prepared for the European Commission by a consortium of companies and research institutions. This study presents a technoeconomic assessment (TEA) of global SFC value chains and pathways for sustainable implementation, estimating the levelized cost of energy (LCOE). Only the multistep production of SFCs was considered, e.g., energy production (by PV or wind), H2 generation (by three types of electrolyzers) or PEC, and the production of methanol or methane (by CO2 thermocatalytic hydrogenation) or ethanol (by microalgae). The study indicates that (i) the cost of producing green H2 is the most significant component of the LCOE, while being highly dependent on renewable electricity and CAPEX costs, and (ii) microalgae technology has a high LCOE, primarily due to very high CAPEX. What emerges from this analysis, even if not explicitly stated, is the need (to create competitive SFCs) to move to a second generation of technologies compared to those analyzed in the study, e.g., those that do not pass through H2 formation as an intermediate. The future of SFCs depends on low-cost, distributed technologies that utilize direct solar energy, such as APDs, with a low CAPEX design (different from the finalized-to-performance design) that additionally avoids costly upstream and downstream processing.

While gap analysis studies focus on current technologies, it is necessary to conduct a perspective gap analysis to identify how to overcome current limitations by fostering more disruptive technologies. The LCOE analysis of the current pathways and technologies shows that energy input costs are the key driver of technologies’ market prospects and impact. Therefore, the focus should not be solely on increasing TRL, but rather on accelerating the discovery of novel (2nd-generation) solutions, thereby drastically reducing costs beyond the typical reductions associated with technology development.

3.2. Indications from the Clean Energy Technology Observatory (CETO)

A CETO status report on direct SFCs in the European Union analyzes the technological developments, trends, value chains, and the market. The following report further compares SFCs with e-fuels, where the first step is the electrolytic H2 production, e.g., direct versus multistep approaches. The primary routes considered are direct photochemical and photobiological processes as well as indirect solar thermochemical processes. The main challenges identified are stability, scale-up, efficiency, and continuous operation; however, insufficient benchmarking protocols and standards are also noted. Additionally, the lack of unique metrics and protocols to comparatively assess the status and prospects of various technologies was remarked upon. Figure reports the estimated technology readiness level (TRL) for 2019 and the forecast for 2030 for technologies producing green H2, ammonia, and chemicals/fuels. The error bars reflect the uncertainty in TRL estimations, current and forecast. The width of the horizontal bars indicates the expected degree of technology development over a decade, i.e., the potential for improvement in TRL. Even with some uncertainties, Figure indicates an expected rapid growth in technologies related to SFCs, with some at TRL 9 and others at TRL 6–7 already by 2030. The estimated potential markets are nearly 300 Mtoe. , The following emerging trends are identified: (i) biohybrid approaches, (ii) capture and direct conversion of CO2 in a single device, (iii) novel device approaches, and (iv) solutions for full circularity.

1.

1

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Assessment of the technology readiness level for sustainable solar hydrogen, ammonia, chemicals, and fuels. Elaborated from the original table in ref .

A series of key enabling technologies (KETs) are indicated. , They are summarized in Table , which presents a matrix of technologies versus main KETs classified into four groups: materials, devices, systems, and fundamental knowledge. These KETs represent a gap analysis to be combined with the indications in Figure . In the sustainable production of chemicals and fuels, PEC devices and biocatalytic routes were forecast to achieve an impressive increase in TRL, from 5 to 6 levels over a decade. In comparison, direct solar–thermochemical conversions were expected to increase by only 1–2 TRL levels. The gaps (KETs) in the latter are thus considered more challenging to address than those in the other two areas.

1. Key Enabling Technologies (Gap Analysis) for Sustainable Solar Hydrogen, Ammonia, Chemicals, and Fuels .

  materials devices system fundamentals
Green H2
advanced electrolysis (PV-driven) no CRM automated manufacturing system integration  
photoelectrochemical devices no CRM (not toxic) photon management autoassembly and charge photoaccumulation and transfer processes nonadiabatic conversion; bioinspiration
catalysts and semiconductors
self-repair/self-healing responsive matrices and interfaces
transparent baggie systems (microorganisms and photocatalytic systems) materials science and development photobioreactor design system engineering understanding of the natural photosynthesis and cell metabolism
enzyme chemistry photon management advanced theoretical and experimental techniques
Green NH3
low-emission Haber–Bosch (with green H2) bioinspired catalysts for N2 reduction green hydrogen production high-throughput computing  
electrochemical and plasma-assisted ammonia synthesis electrochemical NRR photo(electro)chemical devices direct solar water splitting  
microorganisms for direct fertilizer production nitrogenase biomimicking (ATP-independent and O2-resistant) systems     new metabolic engineering strategies
Sustainable chemicals and (jet) fuels
electrochemical water splitting and thermocatalytic conversion of CO2 (two-stage process)   multiscale modeling for thermochemical electrically heated reactors system engineering for dynamic life-cycle cost analysis ab initio modeling and high-throughput screening
advanced manufacturing for new reactor concepts system engineering
direct electroreduction of CO2 ab initio modeling and high-throughput screening (catalyst development) multiscale modeling system engineering in operando analytical tools
life-cycle cost analysis
direct solar–thermochemical conversion of water and CO2 materials engineering membrane technologies smart process control and interfaces  
materials research with ab initio modeling and experimental screening
solid particle technologies
photo(electro)chemical devices   advanced photo(electro)chemical devices    
biocatalytic production of carbon-based solar fuels and chemicals strain characterization and optimization cost-efficient photobioreactors efficient engineering and synthetic biology tools  
engineered new strains with enhanced metabolic pathways upscaling, including cheap bioreactor and downstream processing improved photosynthetic performance and carbon metabolism
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a

It was adapted from the CETO reports on solar fuels. ,

3.3. Japanese Apollo Project

The “Japanese Apollo Project” is a very recent governmental initiative aimed at fostering APDs, resulting in a roadmap released in September 2025. It is the result of a study involving both Japanese and foreign experts to chart a path forward in APDs. It plans to foster public and private investments, aiming to revitalize Japan’s economy. The milestones for social implementation are summarized in Figure . By 2030, a proof of concept for specific products using mature electrolytic processes to split CO2 and water is forecast. By 2025, more efficient “coelectrolysis” technologies are expected. Finally, by 2040, mass production of base materials will be intended to expand the product portfolio. This roadmap identifies advances in electrocatalysis and photocatalysis as being critical. In the SI, additional figures detailing the roadmap, organized into two main areas of elemental technology (electrolytic and photocatalytic systems), and comments on roadmap indications are provided.

2.

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Translated from the Japanese “Artificial Photosynthesis Roadmap toward Social Implementation” (Apollo Project). Presented on Sept. 2, 2025.

3.4. SUNERGY/SUNER-C Roadmap and Blueprint Map

SUNER-C in an EU Coordination and Support Action (project 101058481, ended June 2025) is powered by the SUNERGY Community, whose goal was to work together on building an ecosystem to accelerate the introduction of SFCs and APDs (https://sunergy-initiative.eu/suner-c). As part of the project, (i) a Strategic Research and Innovation Agenda on Solar Fuels and Chemicals (SRIA), (ii) a technological roadmap, and (iii) a blueprint report of SFCs and APDs, which includes key performance indicators (KPIs), were prepared.

The complex ecosystem of SFCs and APDs was structured by analyzing the energy conundrum, as summarized in Figure .

3.

3

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Energy conundrum in the SF and APD area as presented in the SUNERGY/SUNER-C Technology Roadmap (June 2025). It depicts the converging technology areas with the artificial photosynthesis (or artificial leaf) concept. Gert Jan Kramer (Copernicus Institute of Sustainable Development, Utrecht, The Netherlands) conceived this comprehensive approach and published it in a book chapter.

The Technology Roadmap (https://sunergy-initiative.eu/wp-content/uploads/2024/05/D7-D3.1-Technological-roadmap.pdf) provides an updated state-of-the-art piece in the field and analyzes the technical and sustainability goals and challenges, offering strategic insights. For example, regarding electrochemical technologies, it is indicated that 2035 is the year when the first industrial, first-of-a-kind implementations for C1 carbon molecules (such as CO and formates) and industrial demonstrators for C2 carbon molecules (such as ethylene and ethanol) may be completed. Both are expected to be industrially and technically relevant by 2050. Meanwhile, bioelectrolysis and low-temperature ammonia conversion will still require R&D efforts to be ready for piloting after 2035. The photo­(electro)­chemical domain remains underdeveloped due to the field’s relative immaturity. A KPI analysis of the various paths was provided in the blueprint report (https://sunergy-initiative.eu/wp-content/uploads/2025/06/D8-D3.2-Blueprint.pdf).

The latter focuses on the concrete steps required to ensure that critical hurdles on the way to coupling solar to chemistry and DAC (direct air capture) are successfully addressed. It thus complements the technological roadmap well. Note, however, that solar H2 technologies are also considered part of the technological pipeline, whereas we do not consider them among the APDs, see the introduction. The blueprint report also lists a series of KPIs (key performance indicators) to monitor and compare different technologies.

3.5. An Academic Roadmap

Unlike other roadmaps that aim to represent the open effort of a community, the roadmap paper of Segev et al. on SFCs reflects (mainly) the personal opinions of the participating authors. It lacks essential elements such as a strategic vision, indications on timing, and a gap analysis. The topics addressed are diverse, ranging from electrocatalysts to methods for benchmarking efficiency and stability, yet there is no unique, coherent link among them. They identify three design levels for SFC production, e.g.,

  • 1)

    the device (limited to benchmarking and scale-up, not considering system integration, impact, and other crucial aspects); often, the downstream processes are a very relevant cost factor;

  • 2)

    the electrodes and membranes (addressing only marginally the crucial issue of how to design electrodes and reactors in an integrated manner to minimize resistances, the role of mass/electron transport limitations in determining the paths of reaction, the role of a proper choice of the reactors, and operative conditions to perform the tests);

  • 3)

    the atomic-scale electrochemical processes (limited to OER, HER, and CO2RR mechanisms, without assessing whether the current mechanistic approaches, including theoretical modeling, provide relevant indications for improving performance under industrially relevant conditions).

Efficiency, selectivity, lifetime, and scalability are general scientific challenges common to all areas of catalysis. Table S1 summarizes the challenges and the S&T advances required to address them. It provides a good snapshot of the current research directions in SFs and AP devices. However, a critical approach in analyzing indications is recommended.

4. Emerging Trends from the Literature, Patents, and Research Projects

As indicated in the introduction, this section does not aim to provide a comprehensive analysis and discussion of the literature and patents on APDs and SFCs. Instead, the aim is to complement the indications emerging from the previous analysis from these perspectives.

4.1. A Concise Patent Analysis

A patent analysis was conducted using the keyword “solar fuel” in the Espacenet patent database to identify development trends in SFCs from an application perspective. The search focuses on patent families to avoid bias introduced by counting the same invention multiple times. Only patents in English were considered, with the keyword in the title or abstract. The first patent families related to solar fuels were filed as early as 2004, but their number only grew significantly in the past decade (Figure a). Around 110 patent families in total from 2004 to 2022 (in English; about 60 additional in other languages) contain the keyword “solar fuels”. The countries of these parent families (Figure b) are primarily China and the US, with a minor role for European countries. Only about 10% of the applicants are companies. Some interesting indications emerge when comparing these results with the number of publications and citations obtained from the Exaly database using the keyword “solar fuel” (as a term). The search is based on primary keywords that highlight the paper’s central theme, excluding terms that are only marginally mentioned.

4.

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(a) Total (cumulative) patents (families, in English) versus publications and citations for the keyword “solar fuel” based on indications from Espacenet and Exaly databases (see the text). (b) Patent (family) distribution for country publication (including WO and EP).

In contrast to the rapid increase in publications and citations, the trend in patents follows a more linear growth. This result indicates that “solar fuels” remains mainly an academic field and that scientific progress is still disconnected from the ability to translate results into patents and applications. These results are further supported by Figure , which reports an analysis of the h-index for the EU and leading countries and regions. The h-index indicates that at least h articles in that country for that topic were cited at least h times each. Thus, this shows the number of scientific publications in that country or region receiving significant attention from the scientific community. The typology of SFs structures the ranking.

5.

5

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Analysis of the h-index of the EU and the leading countries and regions. Based on the data in the report on “Direct Solar Fuels in the European Union”. Note that the database used for these data (JRC’s Technology Innovation Monitor system) is different from that used in Figure for publications (Exaly), and a combination of keywords was used. However, the data for the two methods are consistent. The h-index refers to the period 2010–2022 and indicates that at least h articles in that country for that topic were cited at least h times each.

The result emerging from Figure , in comparison with Figure b, is that research on SFs in Europe (particularly in Germany, whose number of publications is about three times those of France, which is in second place in the EU, followed by Italy, Spain, Sweden, and The Netherlands, in that order) is well-aligned to those in countries such as the US and China. However, this scientific quality and effort do not reflect an equivalent impact on patents and applications. There is thus a gap between translating research into practice in Europe.

Using the keyword “artificial photosynthesis”, around 260 patent families are reported in the Espacenet patent search database, with over twice that for the solar fuel keyword. In this case, Japan becomes the second country after China and before the US. Only 13 entries are related to the keyword “artificial photosynthesis device” and 52 to “photoelectrochemical device”. The research also has mainly academic character for these topics, and the number of companies among the applicants is limited.

4.2. A Status Analysis from the Literature

For the sake of conciseness, this part is discussed in the SI; however, it is not intended to be a precise state-of-the-art review. The aim is to present the necessary complements to the other assessments reported in this perspective.

The general conclusion from the gap analysis literature (SI) is that it reflects current scientific trends that do not necessarily align with the critical gaps needed for implementation. A critical comparative analysis is rarely conducted, and several crucial questions remain unanswered. A more critical comparative gap analysis of the specific scientific interest is necessary to define unconventional directions and bridge the gap to application. This approach does not rely on the linear improvement of current methodologies but requires a breakthrough effort toward new research paths. ,−

4.3. Hot Research Themes from an Analysis of Running Projects

For conciseness, this section is also reported in the SI, where a discussion on the status of prototype development and emerging indications on the assessment of selected EU projects on SFs and AP devices is provided. Based on the energy conundrum structuring vision of the SF and APD area (Figure ), a classification of the main EU-funded projects is also reported in the SI. There is an open innovation community of approximately 7000 in the EU research area, with total investment exceeding €200 million, highlighting significant scientific interest. However, due to the lack of effective structuring and organization of the effort, along with the Japanese example, the effective translation of research into innovation and application is slower than expected based on roadmap exercises.

5. Conclusions and Recommendations

Several aspects emerged from this comparative analysis of the prospects for SFCs and APDs. Significant discrepancies exist in the impact in a medium- to long-term scenario up to 2050. We suggest that these discrepancies are mainly related to the capability to predict and account for future scenarios and to the R&D’s ability to overcome scientific/technological gaps. A more critical and holistic analysis of the gaps and research priorities should be undertaken. Often, the topics indicated (see Table S1, for example) refer to specific research interests rather than to a proper gap analysis or axiomatic design.

The analysis of research trends emerging from projects, particularly the more innovative ones, and status reports on SFCs (Table S2) highlights the need to focus research on exploring aspects beyond those noted in academic roadmaps and gap analyses (summarized in Table S1). Better, more defined KPIs, as outlined in the blueprint study in Section , are necessary. Nevertheless, a direct experimental comparison of the APD technologies reveals surprise and a lack of reliable data in the literature. Developing a technological platform to test the proposed technologies is essential to accelerate progress.

The scale-up of devices and thus the increase in TRL progress slowly, as shown in the SI. An advantage of APDs is that scaling is based on numbering rather than size, unlike in conventional chemical plants. Thus, a much faster time-to-market and the ability to adapt to different requirements are possible. However, the design and engineering are different and insufficiently addressed, including in terms of the value chain. Scaling by concentration, such as using sunlight concentration up to relatively modest values (<50 SUN), is another relevant possibility, not addressed, but indicated, for example, by axiomatic design. There are thus peculiarities in scaling APDs that differentiate them from conventional chemical plant scaling practices but are insufficiently addressed.

Cost (TEA) and environmental impact (LCA) are critical aspects for each technology under development. However, for SFCs and APDs, the literature contains unsatisfactory estimates, as these studies should better account for the rapidly evolving value chain and demand landscape arising from the ongoing energy transition. These methodologies should thus be used to identify the critical factors for improvement rather than to rank these technologies against others.

Although progress has been made on second-generation (direct) technologies for SFCs (see the SI), a gap toward application persists, which widens with more demanding applications, e.g., passing from H2 production to CO2RR and NRR. While fundamental studies (summarized in Table S2) will progressively reduce the gap, the innovation rate should be accelerated by instead broadening technology options and passing to next-generation (direct, integrated) solutions.

Analyzing gaps and priorities in SFCs and APDs also suggests the need to rethink fundamental research strategies and priorities. Learning from nature from a smart perspective is the key challenge. There are two possible indications, among others, of this challenge. The first is a systemic approach based on axiomatic design that analyzes and implements bottom-up engineering of a final device by transferring nature-based mechanisms and functions to artificial photo­(electro)­catalytic systems. This approach will provide strict guidance for optimizing modular function via molecular and interface modification and integration into a device.

The second possible advanced biomimetic approach is based on the design of multimetal cores integrated with their surrounding environment, which serves as a cocatalyst. There have been initial attempts in this direction, for example, the emerging concept of “artificial quantasomes”. These are just a few examples. Still, they highlight the need to approach the idea of learning from nature from a different perspective to design more effective APDs.

Regarding photo- and electrocatalysts, there is also a need to rethink the current approach and design conceptually novel electrodes. Mechanistic features and engineering aspects differentiate photo- and electrocatalysis from conventional catalysis but are insufficiently addressed, leading to ineffective design.

In conclusion, this critical comparative analysis of findings from research projects, patents, roadmaps, status reports, and the literature provides several relevant insights for both the research community and the agencies that finance research in SFCs and APDs. The general indication is to make a quantum leap in research topics and priorities to accelerate the effective use of APDs. If this could be realized, SFCs and APDs will play a significant role in a decarbonized future.

Supplementary Material

af5c00034_si_001.pdf (2MB, pdf)

Acknowledgments

Carina Faber and Francesco Matteucci of the European Innovation Council and the Small and Medium Enterprise Agency (EIC-EISMEA), European Commission, Brussels (Belgium), are acknowledged for their contributions to preparing this manuscript.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/aps.5c00034.

  • Series of aspects, discussions, tables, and figures that complement and integrate those presented here; a final appendix section reporting general aspects beneficial for nonspecialists; and a list of the abbreviations used (PDF)

The manuscript was written with contributions from all authors. All authors have approved the final version of the manuscript.

G.C. and S.P. thank the ERC Synergy SCOPE (project 810182), ERC PoC SOLAR-H2 (project 101247232), EU project SUNER-C (project number 101058481), and PRIN 2022 project MATISSE (project number 2022K5SX27_002) for financial support.

The authors declare no competing financial interest.

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