Trends in Chemistry
Volume 2, Issue 1, January 2020, Pages 57-70
Journal home page for Trends in Chemistry

Review
Emerging Photocatalysts for Hydrogen Evolution

https://doi.org/10.1016/j.trechm.2019.06.009Get rights and content

Highlights

  • Photocatalytic H2 evolution from water is a promising avenue for the sustainable production of clean fuels without byproduct pollutants as in the traditional use of fossil fuels.

  • Three water-splitting routes (i.e., POWS, PPWS, and PIWS) have been developed for photocatalytic H2 evolution that involve light-absorption, charge-transport, and surface-reaction processes.

  • A range of cost-effective photocatalysts and cocatalysts have been developed for higher-efficiency H2 evolution. Steady progress on efficiency, scalability, and operability has been achieved towards large-scale H2 production.

Hydrogen evolution via solar-driven photocatalytic water splitting (PWS) is considered an important strategy for facilitating clean global energy and overcoming the severe environmental challenges facing our society. As a result, many photocatalysts have been developed over the past several years. In this review, we outline the most recent advances in hydrogen evolution photocatalysts over the past 2 years. In particular, we introduce hydrogen production methods, main and cocatalysts for hydrogen evolution through water splitting, the underlying photocatalytic mechanisms, and current challenges and future potential advances for this exciting field.

Section snippets

Hydrogen Evolution via PWS

Concerns regarding the depletion of fossil fuels and the increase of environmental pollution have aroused a sense of urgency in developing renewable and clean energy technologies. Hydrogen gas (H2) has been regarded as one of the cleanest energy carriers for such purposes, since when used in a fuel cell, for example, it produces only water, electricity, and heat. However, H2 is primarily created by energy-consuming and environmentally unsustainable hydrocracking of fossil fuels through refinery

Fundamentals of H2 Evolution from PWS

Ideally, H2 evolution from PWS is based on the fact that water is split directly into H2 and O2 on the surface of a photocatalyst (e.g., a semiconductor) 5, 6. For reference, Box 1 summarizes the three major steps underlying PWS. Thermodynamically, water splitting is a four-electron process, requiring a Gibbs free energy of 237 kJ mol-1 7, 8, 9, 10, 11 that corresponds to 1.23 eV and ∼1000 nm in wavelength for light activation. Therefore, >50% of energy is available from natural sunlight for

Semiconductors

Semiconductors are the most widely investigated photocatalysts [51]. The chemical composition, electronic band structure, and morphology significantly affect the resulting catalyst performance. In the various kinds of metal-based semiconductor photocatalysts, metal cations with d0 or d10 electronic configurations are usually introduced to construct CBs, whereas the VBs usually comprise nonmetal elements (e.g., N, O, S, Se).

Cocatalysts for Photocatalytic H2 Evolution

Reduction cocatalysts are commonly used for photocatalytic H2 evolution to provide redox reaction sites and lower activation energies. Noble metals (e.g., Pt, Rh, Pd) are widely used [19]; however, their scarcity largely limits their promise towards large-scale, practical applications. Accordingly, various non-noble metal cocatalysts have been explored as alternatives. Metal chalcogenides (e.g., MoS2, NiS, CuS) have emerged as promising cocatalysts [55]. Excellent H2-evolution kinetics are

Improving Key Contributors to Photocatalytic H2 Evolution

Photocatalytic H2 evolution depends strongly on the photocatalyst light-absorption, charge-transfer, and surface-reaction properties. In this section, we briefly describe recent progress on improving these key properties.

Photocatalytic H2-evolution activity is strongly related to catalyst light absorption, which dictates the number of excited charges created for all of the photocatalytic reactions. Dopants, dye sensitizers, and defect-related color centers are widely used to enhance light

Concluding Remarks

In recent years, considerable progress has been made in photocatalytic H2 evolution. However, several critical scientific challenges remain in the areas of efficiency improvement, mechanistic understanding, and practicality for both fundamental research and large-scale photocatalytic H2 evolution (see Outstanding Questions). Of course, a major goal is it to achieve continuous, high-efficiency, and sustainable photocatalytic H2 evolution from water without the assistance of electron donors and

Acknowledgments

This work was supported by the Natural Science Foundation of China (No 21703046) and the Ministry of Science and Technology of China (No 2016YFF0203803 and 2016YFA0200902). X.C. appreciates support from the US National Science Foundation (DMR-1609061) and the College of Arts and Sciences, University of Missouri-Kansas City.

References (90)

  • Y. Si

    What is the predominant electron transfer process for Au NRs/TiO2 nanodumbbell heterostructure under sunlight irradiation?

    Appl. Catal. B

    (2018)
  • S. Cao

    Ultrasmall CoP nanoparticles as efficient cocatalysts for photocatalytic formic acid dehydrogenation

    Joule

    (2018)
  • N.S. Lewis

    Developing a scalable artificial photosynthesis technology through nanomaterials by design

    Nat. Nanotechnol.

    (2016)
  • J. Li

    Frontiers of water oxidation: the quest for true catalysts

    Chem. Soc. Rev.

    (2017)
  • N. Serpone

    Why do hydrogen and oxygen yields from semiconductor-based photocatalyzed water splitting remain disappointingly low? Intrinsic and extrinsic factors impacting surface redox reactions

    ACS Energy Lett.

    (2016)
  • Y. Xu

    Metal-free carbonaceous electrocatalysts and photocatalysts for water splitting

    Chem. Soc. Rev.

    (2016)
  • A. Fujishima et al.

    Electrochemical photolysis of water at a semiconductor electrode

    Nature

    (1972)
  • J. Low

    Heterojunction photocatalysts

    Adv. Mater.

    (2017)
  • X. Chen

    Semiconductor-based photocatalytic hydrogen generation

    Chem. Rev.

    (2010)
  • L. Wang

    2D polymers as emerging materials for photocatalytic overall water splitting

    Adv. Mater.

    (2018)
  • K. Wu et al.

    Quantum confined colloidal nanorod heterostructures for solar-to-fuel conversion

    Chem. Soc. Rev.

    (2016)
  • M. Rahman

    Carbon, nitrogen and phosphorus containing metal-free photocatalysts for hydrogen production: progress and challenges

    J. Mater. Chem. A

    (2018)
  • K. Takanabe

    Photocatalytic water splitting: quantitative approaches toward photocatalyst by design

    ACS Catal.

    (2017)
  • J. Liu

    Metal-free efficient photocatalyst for stable visible water splitting via a two-electron pathway

    Science

    (2015)
  • T. Hisatomi

    Photocatalytic water-splitting reaction from catalytic and kinetic perspectives

    Catal. Lett.

    (2015)
  • T. Hisatomi

    Recent advances in semiconductors for photocatalytic and photoelectrochemical water splitting

    Chem. Soc. Rev.

    (2014)
  • F.A. Chowdhury

    A photochemical diode artificial photosynthesis system for unassisted high efficiency overall pure water splitting

    Nat. Commun.

    (2018)
  • Q. Wang

    Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1%

    Nat. Mater.

    (2016)
  • T.H. Chiang

    Efficient photocatalytic water splitting using Al-doped SrTiO3 coloaded with molybdenum oxide and rhodium−chromium oxide

    ACS Catal.

    (2018)
  • J. Yang

    Roles of cocatalysts in photocatalysis and photoelectrocatalysis

    Acc. Chem. Res.

    (2013)
  • S. Cao

    Metal phosphides as cocatalysts for photocatalytic and photoelectrocatalytic water splitting

    ChemSusChem

    (2017)
  • B. Qiu

    Efficient solar light harvesting CdS/Co9S8 hollow cubes for Z-scheme photocatalytic water splitting

    Angew. Chem. Int. Ed. Engl.

    (2017)
  • L.K. Preethi

    A study on doped heterojunctions in TiO2 nanotubes: an efficient photocatalyst for solar water splitting

    Sci. Rep.

    (2017)
  • R. Shi

    Interstitial P-doped CdS with long-lived photogenerated electrons for photocatalytic water splitting without sacrificial agents

    Adv. Mater.

    (2018)
  • A. Meng

    Dual cocatalysts in TiO2 photocatalysis

    Adv. Mater.

    (2019)
  • X. Cai

    Ultrafast charge separation for full solar spectrum-activated photocatalytic H2 generation in a black phosphorus−Au−CdS heterostructure

    ACS Energy Lett.

    (2018)
  • K. Mase

    Seawater usable for production and consumption of hydrogen peroxide as a solar fuel

    Nat. Commun.

    (2016)
  • P. Kalisman

    Perfect photon-to-hydrogen conversion efficiency

    Nano Lett.

    (2016)
  • T. Uekert

    Plastic waste as a feedstock for solar-driven H2 generation

    Energy Environ. Sci.

    (2018)
  • S. Cao

    Cobalt phosphide as a highly active non-precious metal cocatalyst for photocatalytic hydrogen production under visible light irradiation

    J. Mater. Chem. A

    (2015)
  • Z. Wang

    Recent developments in heterogeneous photocatalysts for solar-driven overall water splitting

    Chem. Soc. Rev.

    (2019)
  • K. Sayama

    Production of high-value-added chemicals on oxide semiconductor photoanodes under visible light for solar chemical-conversion processes

    ACS Energy Lett.

    (2018)
  • L. Liao

    Efficient solar water-splitting using a nanocrystalline CoO photocatalyst

    Nat. Nanotechnol.

    (2014)
  • H. Fujito

    Layered perovskite oxychloride Bi4NbO8Cl: a stable visible light responsive photocatalyst for water splitting

    J. Am. Chem. Soc.

    (2016)
  • X. She

    High efficiency photocatalytic water splitting using 2D α-Fe2O3/g-C3N4 Z-scheme catalysts

    Adv. Energy Mater.

    (2017)
  • Cited by (135)

    View all citing articles on Scopus
    View full text