1. A unique rare-earth-regulated “all-in-one optimization” strategy was proposed for the first time to develop an ideal photocatalytic CO₂ methanation system.
2. The optimized TiO₂-Cu₇Pr₁ catalyst delivered exceptional photocatalytic activity, achieving an electron selectivity toward CH₄ of 96.6% and a CH₄ production rate of 792.6 μmol g−1 h−1.
3. Comprehensive experiments and DFT calculations confirmed that rare-earth regulation creates multiple favorable conditions for different elementary steps of the photocatalytic process.
In March 2026, the Journal of Energy Chemistry published online the latest research achievement in photocatalytic CO₂ reduction from Professor Yinlong Zhu’s team at Nanjing University of Aeronautics and Astronautics. The study reports a unique rare-earth-regulation strategy that synergistically optimizes light absorption, charge separation, reactant supply, and active sites throughout the photocatalytic process, resulting in a CO₂ methanation photocatalyst that simultaneously delivers high activity, high selectivity, and excellent stability. The first author is Zhongliang Dong, and the co-corresponding authors are Professor Yanpeng Liu and Professor Yinlong Zhu.
Solar-driven photocatalytic reduction of CO₂ into high-value-added hydrocarbon fuels, such as methane, is an ideal approach for mitigating the energy crisis and greenhouse effect. However, photocatalytic CO₂ methanation is a complex process involving multiple electron–proton transfer steps. Its efficiency is restricted by poor light-harvesting capability, inefficient charge-carrier separation, difficult reactant adsorption and activation, and slow surface-reaction kinetics.
Existing modification strategies often optimize only one specific step and therefore struggle to achieve synergistic enhancement across the entire reaction process. Developing an “all-in-one optimization” strategy capable of simultaneously improving each elementary step of the photocatalytic reaction is therefore highly important for efficient CO₂ methanation.
Figure 1. Conceptual Illustration and Structural Characterization
Different molar ratios of Cu/Ln atoms, where Ln represents La, Ce, Pr, Nd, Sm, or Gd, were loaded onto TiO₂ substrates through a photo-induced deposition method, successfully producing a series of TiO₂-CuxLny nanocomposite photocatalysts. Among them, TiO₂-Cu₇Pr₁ exhibited the highest photocatalytic CO₂-reduction activity and was therefore selected as the model catalyst for systematic structural characterization.
High-resolution transmission electron microscopy images revealed ultra-small spots with an average size of approximately 1.88 nm distributed over the TiO₂ surface. Lattice fringes corresponding to the (111) plane of hexagonal Cu₇Pr₁ alloy were observed, confirming the formation of Cu₇Pr₁ alloy quantum dots. High-angle annular dark-field scanning transmission electron microscopy and EDS elemental mapping further showed 1–2 nm nanoparticles and concentrated distributions of Cu and Pr, confirming that the alloy quantum dots were stably anchored on the TiO₂ surface.
The quantum-dot modification slightly increased the BET specific surface area, which helped expose additional active sites. Although characteristic diffraction peaks of the CuxPry alloy were not detected by XRD because of the low loading and high dispersion, ICP-OES analysis showed that the actual Cu/Pr composition closely matched the theoretical design, demonstrating the excellent flexibility and precision of the photo-induced deposition strategy for controlling elemental ratios.
Figure 2. Photocatalytic CO₂-Reduction Performance
The CO₂-reduction performance of TiO₂-CuxPry photocatalysts with different Cu/Pr molar ratios was systematically evaluated without sacrificial agents. CH₄ was the major carbon-containing product for all catalysts. The optimized TiO₂-Cu₇Pr₁ exhibited the best catalytic activity, with a CH₄ production rate approximately 22.4 times higher than that of monometal-modified TiO₂-Cu and an electron selectivity of up to 96.6%.
The low activity of Cu-free and Pr-rich samples indicates that Cu sites are the principal active centers for CO₂ methanation. Although Pr does not directly participate in the reaction, it substantially enhances the catalytic capability of Cu by regulating the electronic structure of the alloy. Stoichiometric O₂ evolution was also detected, confirming rapid consumption of photogenerated holes and efficient charge separation.
To verify the universality of rare-earth regulation, the same alloying strategy was extended to La, Ce, Nd, Sm, and Gd. All TiO₂-Cu₇Ln₁ catalysts exhibited higher activity and CH₄ selectivity than TiO₂-Cu. A series of control experiments ruled out non-photocatalytic interference and confirmed that the products originated from light-driven CO₂ reduction coupled with water oxidation.
No obvious activity decay or color change was observed during a 72-hour continuous cycling test. Post-reaction XPS, XRD, and STEM analyses showed that the Cu₇Pr₁ alloy structure possessed excellent physicochemical stability, maintained Cu in its metallic state, and suppressed nanoparticle aggregation and phase transformation, thereby enabling durable and highly efficient photocatalytic performance.
Figure 3. Electronic-Structure Analysis
To identify the electronic origin of the excellent photocatalytic CO₂-methanation activity of TiO₂-Cu₇Pr₁, the samples were systematically investigated using XPS and synchrotron XAS. The results clarified the key role of rare-earth Pr in regulating both active sites and support defects.
XPS analysis showed that oxidized Cu²⁺ and Pr³⁺ species dominated in TiO₂-Cu and TiO₂-Pr, whereas only metallic Cu⁰ and Pr⁰ were present on the surface of TiO₂-Cu₇Pr₁. This pronounced oxidation resistance was attributed to strong electronic coupling between Cu and Pr. In addition, the Ti 2p binding energy shifted significantly toward lower values in Pr-containing samples, indicating that Pr-induced strong metal–support interactions reduced the oxidation state of Ti and, according to charge-neutrality requirements, generated a high concentration of oxygen vacancies. This conclusion was further supported by EPR measurements and O 1s peak fitting.
Synchrotron XAS precisely resolved the local coordination environment. Cu K-edge XANES and EXAFS spectra showed that all rare-earth-modified samples exhibited absorption features similar to metallic Cu foil. TiO₂-Cu₇Pr₁ had the strongest Cu–Cu bonding and the highest proportion of metallic Cu⁰. The Cu⁰ content correlated positively with methanation activity, confirming metallic Cu as the central active site for converting CO₂ to CH₄.
Quantitative fitting of Ti EXAFS data showed that rare-earth alloy modification reduced the Ti–O coordination number in the first coordination shell, providing atomic-scale structural evidence that Pr promotes oxygen-vacancy formation. Overall, Pr may enhance reactant enrichment and activation through the dual synergistic effects of stabilizing metallic Cu⁰ active species and inducing abundant oxygen vacancies.
Figure 4. Reactant Supply and Light-Absorption Behavior
Strong CO₂ adsorption and effective water activation are critical for producing high-value carbon products during photocatalytic CO₂ reduction. CO₂-TPD measurements showed that TiO₂-Cu₇Pr₁ possessed the strongest chemisorption strength and the highest adsorption capacity, with a peak desorption temperature of approximately 514.1 °C. Combined with calculated adsorption energies, the results indicate that this superior adsorption originates from the synergistic effect of abundant oxygen vacancies and rare-earth alloy modification, which greatly enhances stable anchoring of CO₂ on the catalyst surface.
Water-contact-angle measurements and kinetic analysis showed that the introduction of alloy quantum dots improved surface hydrophilicity. Oxygen vacancies also reduced the reaction barrier for water dissociation, namely O–H bond cleavage, to 0.34 eV, accelerating proton supply and providing sufficient hydrogen for highly selective methanation.
Regarding solar-energy utilization, fine regulation of the band structure was achieved by controlling the Cu/Pr ratio in the alloy. UV–visible diffuse-reflectance spectra and density-of-states calculations consistently showed that the light-absorption intensity increased progressively with increasing Cu content. Theoretical calculations attributed this behavior to strong hybridization between Cu 3d and Pr 4f orbitals. This orbital coupling effectively narrowed the intrinsic band gap and optimized the photoresponse range.
Figure 5. Charge-Carrier Separation and Transfer Behavior
Multiple characterization techniques and systematic theoretical calculations revealed the dynamics of carrier separation and transfer induced by the interfacial electric field. Work-function calculations showed that TiO₂-Cu₇Pr₁ had a work function of 4.68 eV, higher than the 4.61 eV of TiO₂, indicating that electrons tend to migrate spontaneously from the semiconductor to the alloy phase.
KPFM measurements directly confirmed this trend. Under illumination, the surface contact-potential difference of TiO₂-Cu₇Pr₁ reached 195.3 mV, approximately twice that of TiO₂-Cu, demonstrating that the incorporation of rare-earth Pr effectively constructed a strong built-in electric field. Differential charge-density analysis more directly revealed charge redistribution, with charge concentrated at the two-phase interface and within the Cu₇Pr₁ alloy region rather than remaining only on the TiO₂ surface.
The benefits of the strong interfacial electric field were further confirmed by photoelectrochemical tests. TiO₂-Cu₇Pr₁ exhibited the strongest transient photocurrent response and the lowest charge-transfer resistance, while its steady-state photoluminescence signal was almost completely quenched, demonstrating effective suppression of radiative recombination of photogenerated electron–hole pairs.
Femtosecond transient absorption spectroscopy provided ultrafast kinetic evidence for carrier relaxation. The optimized sample displayed the strongest excited-state absorption and significantly shorter decay time constants, indicating that photogenerated electrons were rapidly injected from the TiO₂ conduction band into the Cu₇Pr₁ alloy quantum dots. Overall, the strong Pr-regulated interfacial electric field established an efficient electron-transfer pathway, ensuring that a large number of free carriers participated effectively in the subsequent CO₂ methanation reaction.
Figure 6. Theoretical Calculations and Mechanistic Investigation
Time-resolved in-situ diffuse-reflectance infrared Fourier-transform spectroscopy and DFT calculations were used to systematically investigate the reaction mechanism and electronic origin of photocatalytic CO₂ methanation over TiO₂-Cu₇Pr₁. Dynamic DRIFTS monitoring showed that the reaction proceeded through a pathway involving the key *CHO intermediate: CO₂ → *COOH → *CO → *CHO → CH₄.
Compared with TiO₂-Pr, which mainly produced CO and showed no detectable *CHO signal, and the less-active TiO₂-Cu sample, TiO₂-Cu₇Pr₁ exhibited much faster accumulation of *CHO and *CH₂ intermediates, together with a stronger *OH signal. These results demonstrate the key role of rare-earth Pr in promoting active-hydrogen consumption and accelerating intermediate protonation and conversion.
Theoretical calculations further revealed the enhancement mechanism. Projected crystal orbital Hamilton population analysis showed that Pr incorporation induced unique Pr 4f–Cu 3d orbital hybridization, causing the Cu d-band center to shift upward relative to the Fermi level and significantly strengthening bonding between Cu active sites and the C atom of CHO. The −ICOHP value increased from 1.674 to 1.870.
Electron-localization-function and Bader-charge analyses showed that this electronic regulation strongly localized electrons at the Cu/CHO interface and drove electron transfer from Cu to adsorbed *CHO, thereby promoting the proton-coupled electron-transfer process and substantially lowering the reaction barrier.
In summary, the rare-earth-Pr-based “all-in-one optimization” strategy simultaneously enhanced light absorption, reactant enrichment, charge-carrier separation and migration, and methanation-site activation, successfully constructing a non-noble-metal photocatalytic system with high activity, high selectivity, and high stability.
This study proposes an “all-in-one optimization” design concept based on rare-earth regulation and successfully constructs a TiO₂-Cu₇Pr₁ composite photocatalyst. The catalyst exhibited outstanding activity, high electron selectivity, and excellent long-term stability in CO₂ methanation, outperforming most photocatalytic CO₂-reduction systems reported to date.
Comprehensive experiments and systematic DFT calculations showed that the strategy synergistically regulated the band-gap width, oxygen-vacancy concentration, interfacial electric-field strength, and Cu 3d–Pr 4f orbital coupling. As a result, it simultaneously enhanced light absorption, enriched the reactants CO₂ and H⁺, promoted rapid charge-carrier separation and migration, and created highly active methanation sites.
This work not only provides a high-performance, noble-metal-free nanocomposite catalyst but also opens a new theoretical and technical pathway for designing highly efficient photocatalysts that satisfy multiple ideal performance requirements.
Yinlong Zhu is a professor and doctoral supervisor at the International Frontier Science Research Institute of Nanjing University of Aeronautics and Astronautics. He is a recipient of a national high-level overseas young-talent program, a Jiangsu Distinguished Professor, an Australian Research Council DECRA Fellow, and a recipient of NUAA’s “Chang Kong Talent” program.
He received his Ph.D. in Materials Chemical Engineering from Nanjing Tech University between 2012 and 2017. From 2018 to 2021, he worked as a postdoctoral researcher and project research fellow at Monash University in Australia. In 2022, he returned to China and established the Laboratory of Clean-Energy Catalytic Materials and Devices at NUAA.
His long-term research focuses on new-energy materials and devices, including fuel cells, metal–air batteries, electrocatalysis, and electrosynthesis. He has published more than 90 SCI-indexed papers, including over 60 as first or corresponding author in journals such as Chemical Society Reviews, Nature Communications, Journal of the American Chemical Society, Advanced Materials, and Angewandte Chemie International Edition. His work has received more than 10,000 citations, with an h-index of 51.
As principal investigator, he has led projects funded by the National Natural Science Foundation of China, including overseas-young-talent, General Program, and Young Scientists Fund projects, as well as Australian Research Council DECRA and Discovery projects. His honors include the International Association of Advanced Materials Young Scientist Award, Chemical Communications Emerging Investigator recognition, the Industrial Chemistry & Materials Young Innovator Award, the Australian Research Council Early Career Researcher Award, recognition as a highly cited author by the Royal Society of Chemistry, and inclusion among the world’s top 2% of scientists.
Research Group Website:
https://www.x-mol.com/groups/Zhu_Yinlong
Rare-earth regulatory all-in-one optimization for exceptional photocatalytic CO₂ methanation
Zhongliang Dong, Wenfa Chen, Ruixi Qiao, Yuyang Long, Meipeng Jian, Mingkai Xu, Zheng Tang, Xuchen Nie, Jun Yin, Yanpeng Liu, Zhiwei Hu, Yinlong Zhu
Journal of Energy Chemistry
https://doi.org/10.1016/j.jechem.2026.02.009
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