Cocatalyst For H2 Evolution Research Articles

Decoupling H2 and O2 Release in Particulate Photocatalytic Overall Water Splitting Using a Reversible O2 Binder.

H2 and O2evolutions occur simultaneously for conventional particulate photocatalytic overall water splitting (PPOWS), leading to a significant backward reaction and the formation of an explosive H2/O2 gas mixture. This is an issue that must be addressed prior to industrialization of PPOWS. Here, a convenient, cost-effective, and scalable concept is introduced to uncouple hydrogen and oxygen production for PPOWS. Based on this idea, a three-component photocatalyst, Co(5%)-HPCN/(rGO/Pt), is constructed, consisting of a photoresponsive chip (HPCN), a H2 evolution cocatalyst (rGO/Pt), and a cobalt complex capable of reversibly binding O2 (Co), to achieve the decouplingof PPOWS under alternating UV and visible light irradiations. The asynchronousO2 and H2 evolution strategy have considerable flexibility regarding the photocatalyst structure and light sources suitable for PPOWS.

Simultaneous Structural and Electronic Engineering on Bi- and Rh-co-doped SrTiO3 for Promoting Photocatalytic Water Splitting.

Activating metal ion-doped oxides as visible-light-responsive photocatalysts requires intricate structural and electronic engineering, a task with inherent challenges. In this study, we employed a solid (template)-molten (dopants) reaction to synthesize Bi- and Rh-codoped SrTiO3 (SrTiO3 : Bi,Rh) particles. Our investigation reveals that SrTiO3 : Bi,Rh manifests as single-crystalline particles in a core (undoped)/shell (doped) structure. Furthermore, it exhibits a well-stabilized Rh3+ energy state for visible-light response without introducing undesirable trapping states. This precisely engineered structure and electronic configuration promoted the generation of high-concentration and long-lived free electrons, as well as facilitated their transfer to cocatalysts for H2 evolution. Impressively, SrTiO3 : Bi,Rh achieved an exceptional apparent quantum yield (AQY) of 18.9 % at 420 nm, setting a new benchmark among Rh-doped-based SrTiO3 materials. Furthermore, when integrated into an all-solid-state Z-Scheme system with Mo-doped BiVO4 and reduced graphene oxide, SrTiO3 : Bi,Rh enabled water splitting with an AQY of 7.1 % at 420 nm. This work underscores the significance of simultaneous structural and electronic engineering and introduces the solid-molten reaction as a viable approach for this purpose.

Simultaneous Structural and Electronic Engineering on Bi‐ and Rh‐co‐doped SrTiO3 for Promoting Photocatalytic Water Splitting

AbstractActivating metal ion‐doped oxides as visible‐light‐responsive photocatalysts requires intricate structural and electronic engineering, a task with inherent challenges. In this study, we employed a solid (template)‐molten (dopants) reaction to synthesize Bi‐ and Rh‐codoped SrTiO3 (SrTiO3 : Bi,Rh) particles. Our investigation reveals that SrTiO3 : Bi,Rh manifests as single‐crystalline particles in a core (undoped)/shell (doped) structure. Furthermore, it exhibits a well‐stabilized Rh3+ energy state for visible‐light response without introducing undesirable trapping states. This precisely engineered structure and electronic configuration promoted the generation of high‐concentration and long‐lived free electrons, as well as facilitated their transfer to cocatalysts for H2 evolution. Impressively, SrTiO3 : Bi,Rh achieved an exceptional apparent quantum yield (AQY) of 18.9 % at 420 nm, setting a new benchmark among Rh‐doped‐based SrTiO3 materials. Furthermore, when integrated into an all‐solid‐state Z‐Scheme system with Mo‐doped BiVO4 and reduced graphene oxide, SrTiO3 : Bi,Rh enabled water splitting with an AQY of 7.1 % at 420 nm. This work underscores the significance of simultaneous structural and electronic engineering and introduces the solid‐molten reaction as a viable approach for this purpose.

Optimizing H-adsorption affinity on electron-enriched Pdδ- active sites for efficient photocatalytic H2 evolution

Noble metal Pd is a promising H2-evolution cocatalyst and has attracted expansive attention in photocatalytic water splitting. However, the present H2-production rate of Pd cocatalysts is still limited due to its strong hydrogen adsorption on Pd active sites, resulting in poor hydrogen evolution kinetics. In this work, an electron-enriched Pdδ- modulation strategy is developed to weaken the hydrogen adsorption on Pd active sites by producing PdAu alloy, resulting in an increased H2-production rate. In this case, the PdAu homogeneous alloy with a particle size of 9–20 nm is uniformly deposited on the TiO2 surface to produce PdAu-modified TiO2 photocatalysts (TiO2/PdAu). It is found that the prepared TiO2/Pd79Au21 sample achieves the maximal photocatalytic H2-production performance of 31.98 mmol g-1 h−1, which is 1.53 times higher than that of TiO2/Pd photocatalyst. Experimental and theoretical studies show that in addition to the promoted transfer of photogenerated carriers, the PdAu alloy can spontaneously induce the electron transfer from Au to Pd to form electron-enriched Pdδ- sites, which prominently weakens the Pd-Hads bonds and thus improve the H2-production efficiency. This study provides further insight into the rational optimization of active sites to facilitate the design of efficient photocatalysts.

Ultrafine Rhodium-Chromium Mixed-Oxide Cocatalyst with Facet-Selective Loading for Excellent Photocatalytic Water Splitting.

The development of water-splitting photocatalysts capable of generating green hydrogen (H2) from water and sunlight is crucial for achieving carbon neutrality. Further enhancement of the photocatalytic water-splitting activity is essential to realizing this objective. Photocatalysts with specific exposed crystal facets can facilitate efficient charge separation of electrons/holes, thereby achieving high activity for water splitting. However, there have been no reports of ultrafine (∼1 nm) cocatalysts being loaded onto specific crystal facets of photocatalysts, despite cocatalysts being the actual reaction sites for water splitting. This study establishes a novel method for achieving facet-selective loading of ultrafine H2-evolution cocatalysts onto the {100} facets, which are the H2-evolution facets, of a strontium titanate photocatalyst. The resulting photocatalyst exhibits the highest apparent quantum yield achieved to date for strontium titanate. This research holds the potential to further improve various types of advanced photocatalysts and is expected to accelerate the transition to carbon neutrality.

'Accelerated' Deactivation of Carbon Nitride Photocatalyst for Solar Hydrogen Evolution.

Carbon nitride photocatalysts are among the most studied candidates for efficient solar hydrogen (H2) production due to their abundance of precursors, suitable bandgap, and visible light utilization. However, the polymeric nature of carbon nitride materials raises concerns regarding the self-decomposition during photocatalytic redox processes. Yet, the operational stability of carbon nitride photocatalysts for solar H2 production remains under-explored. Here we evaluate the photostability of carbon nitride photocatalysts with platinum (Pt) as the co-catalyst for solar H2 evolution and significant deactivation of this photocatalyst is observed under'accelerated' testing conditions. It is demonstrated that the detachment of the Pt co-catalyst on the surface of carbon nitride is the major reason for this deactivation, which can be attributed to a synergistic effect of photo-corrosion and mechanical stirring. The photo-corrosion weakens the interfacial bonding between carbon nitride and Pt co-catalyst, while continuous collisions from the mechanical stirring promote the detachment of co-catalysts from the surface of carbon nitride. These understandings provide insights into the rational design of photocatalysts and photocatalytic systems for improved operational stability.

Boosting visible-light-driven photocatalytic H2 production by optimizing surface hydrogen desorption of NiS/CdS–P photocatalyst

Metal chalcogenides are regarded as favorable H2-evolution cocatalysts; however, they often exhibit unfavorable H desorption characteristics due to the strong affinity of nascent H and highly electronegative S sites, which significantly inhibit H2 generation. To address this issue, a general approach to electron-enriched control of sulfur-active sites is developed for weakening the strong interaction of S–H bonds. This is achieved through the formation of a nanostructured model composed of NiS/CdS–P, in which the surface phosphorus (P) atoms are incorporated in CdS NRs to create an imbalanced charge distribution and a localized built-in electric field in the crystal structure of CdS. In this situation, the built-in electric field not only separates the photogenerated electron hole pairs, but it also accelerates the photogenerated electrons from the CdS–P conduction band to the NiS surface for rapid hydrogen reduction rather than hydrogen adsorption. Photocatalytic tests show that the resultant NiS/CdS–P photocatalyst displays a significant H2-generation rate of 44.39 mmol g−1 h−1 and an apparent quantum efficiency of 41% at 420 nm. Valance band XPS analysis shows that CdS–P has a higher electron density than CdS, leading to the production of electron-rich Sδ− active centers. This better photocatalytic hydrogen generation might be due to the synergistic impact of tailoring the intrinsic built-in electric field for the acceleration of photogenerated charges by P-doping and the fabrication of a NiS cocatalyst for hydrogen reduction rather than hydrogen adsorption. The concept of optimizing the electron densities of active sites by morphology tailoring, with an extra built-in electric field, gives a method for rationally constructing artificial photocatalysts for solar power conversion.

Fabrication of CZS NRs/NiSx NPs hybrids with abundant S-vacancies for signally promoting photocatalytic hydrogen production

The cocatalysts play a key role in photocatalytic technology in remarkably improving the efficiency of H2 evolution. Herein, S vacancies-rich Cd0.6Zn0.4S nanorods (CZS NRs) were prepared via solvothermal method. Then, as-obtained CZS NRs were modified with Ni–Co PBA-derived NiSx nanoparticles (NPs) cocatalyst using grinding method. The optimized CZS/NiSx-N-1.5 hybrids (CZS/NiSx-N, where N represents nickel nitrate which was used as nickel source) exhibited outstanding stability and activity, the average rate of H2 was up to 192.82 mmolg−1h−1 in deionized water medium, which was 201.4% higher than that of CZS. Besides, NiSx-A and NiSx-C cocatalysts with different particle sizes were obtained using nickel acetate (A) and nickel chloride (C) as nickel source, respectively. The CZS/NiSx-C-1.5 and CZS/NiSx-A-1.5 exhibited the H2 evolution rate of 180.70 and 201.93 mmolg−1h−1 in deionized water medium, respectively. The as-prepared materials also exhibited the excellent H2 evolution performance in natural seawater medium. Besides, the photocatalytic mechanism of H2 evolution over CZS NRs/NiSs NPs was also discussed. This work develops a novel H2 evolution cocatalyst and unveils the relationship between the loading amount/particle size of cocatalyst on the H2 evolution rate.

Pd(II), Pt(II) metallosupramolecular complexes as Single-Site Co-Catalyst for photocatalytic H2 evolution

Pd(II), Pt(II) metallosupramolecular complexes as Single-Site Co-Catalyst for photocatalytic H2 evolution

Fabrication of NiCo2S4/N-deficient g-C3N4 for efficient photocatalytic H2 production

Graphitic carbon nitride (g-C3N4) as an ideal visible light active photocatalyst has received much attention in the fields of photocatalytic H2 production, pollutant degradation, and CO2 reduction due to its excellent stability and environment friendly features. In this work, g-C3N4 with N-defects (C3N4-x) was obtained through a KOH-assisted hydrothermal strategy followed by a freeze drying and an annealing process using urea as the starting materials. The investigation shows that C3N4-x has a narrower band gap of 2.7 eV, lower zeta potential of -25.9 mV, more negative CB position of -0.97 V and active sites compared to ordinary bulk g-C3N4, these all contribute to the improved activity for photocatalytic H2 evolution. Furthermore, the activity of C3N4-x was further improved by introduction of H2 evolution co-catalyst NiCo2S4 on its surface via a solvent evaporation method. The H2 evolution rate of 20% NiCo2S4/C3N4-x can reach up to 15673 μmol·g−1·h−1 under a 300 W Xe lamp in TEOA solution, which is 92 times for g-C3N4 (170 μmol·g−1·h−1), 46 times for C3N4-x (340 μmol·g−1·h−1), respectively. It is found that the introduction of NiCo2S4 can increase the number of active sites, prolong the carrier lifetime, decrease the H2 evolution potential of the sample, and improve contact between reaction solution and catalyst surface. This work suggests that transition bimetallic sulfides might be suitable H2 evolution co-catalyst for the g-C3N4-based photocatalytic H2 production systems.

Reversing free-electron transfer of sulfide cocatalyst for exceptional photocatalytic H2 evolution

Recently, Yu and co-workers deeply explore the potential impact of free electron transfer between cocatalysts and photocatalyst carriers on H2 evolution efficiency of active sites over MoS2+x. They propose an electron-reversal tactics to evade the unexpected electron transfer and synchronously regulate the above transfer in a beneficial orientation for weakening hydrogen adsorption on S sites. Herein, this highlight not only discusses and summarizes the essences of electron reversal and the optimized H adsorption/desorption mechanism, but also emphasizes the significance of femtosecond transient absorption spectroscopy (fs-TAS) and in-situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) for revealing charge transfer dynamics and processes. We anticipate that this highlight can disseminate a new perspective on the roles of photocatalyst carriers in improving cocatalytic H2-production kinetics.

Construction of Ti3C2/ZnTCPP/CTFs Ohmic/S-scheme hybrid heterojunction with robust built-in electric field for boosting photocatalytic hydrogen evolution

A heterostructure of Ti3C2/ZnTCPP/CTFs was constructed by the freeze-drying method and steam-assisted method. In visible light, the hydrogen evolution rate of Ti3C2/ZnTCPP/CTFs-3 was 6.2 times that of ZnTCPP, 4.4 times that of CTFs, 5.6 times that of Ti3C2/ZnTCPP and 1.7 times that of Ti3C2/CTFs. The hydrogen evolution rate of the optimized ternary composite reached 462.6 μmol·g−1·h−1, and the quantum efficiency at 420 nm was 3.34 %. At the same time, the ternary photocatalyst showed high stability. The strong S-type interfacial electric field promoted the separation of space charges between ZnTCPP and CTFs effectively. The two-dimensional Ti3C2 nanosheets, as an Ohmic-junction H2-evolution co-catalyst, provided more electron transfer pathways and a large number of active sites for photocatalysis. This work provides some new ideas and enlightenment for the rational design of efficient Ohmic/S-scheme heterojunction photocatalysts.

A MOF-derived Bimetallic Co-catalyst for Promoting Visible-light Photocatalytic Hydrogen Evolution on NH2 -MIL-125.

In order to construct noble metal-free co-catalysts to facilitate the transport and separation of photocatalyst carriers, herein, a MOF-based derived bimetallic NiCu0.2 co-catalyst was loaded on NH2 -MIL-125(Ti). The obtained NiCu0.2 /NH2 -MIL-125 exhibited a photocatalytic activity of 161.4 μmol g-1 h-1 for hydrogen evolution, 12.6 times higher than that of the Ni/NH2 -MIL-125 and even slightly better than Pt/NH2 -MIL-125. The work expands the development pathway of cost-effective and highly active bimetallic co-catalysts for photocatalytic H2 evolution.

Rh/Cr2O3 and CoOx Cocatalysts for Efficient Photocatalytic Water Splitting by Poly (Triazine Imide) Crystals

AbstractIn situ photo‐deposition of both Pt and CoOx cocatalysts on the facets of poly (triazine imide) (PTI) crystals has been developed for photocatalytic overall water splitting. However, the undesired backward reaction (i.e., water formation) on the noble Pt surface is a spontaneously down‐hill process, which restricts their efficiency to run the overall water splitting reaction. Herein, we demonstrate that the efficiency for photocatalytic overall water splitting could be largely promoted by the decoration of Rh/Cr2O3 and CoOx as H2 and O2 evolution cocatalysts, respectively. Results reveal that the dual cocatalysts greatly extract charges from bulk to surface, while the Rh/Cr2O3 cocatalyst dramatically restrains the backward reaction, achieving an apparent quantum efficiency (AQE) of 20.2 % for the photocatalytic overall water splitting reaction.

Rh/Cr2 O3 and CoOx Cocatalysts for Efficient Photocatalytic Water Splitting by Poly (Triazine Imide) Crystals.

In situ photo-deposition of both Pt and CoOx cocatalysts on the facets of poly (triazine imide) (PTI) crystals has been developed for photocatalytic overall water splitting. However, the undesired backward reaction (i.e., water formation) on the noble Pt surface is a spontaneously down-hill process, which restricts their efficiency to run the overall water splitting reaction. Herein, we demonstrate that the efficiency for photocatalytic overall water splitting could be largely promoted by the decoration of Rh/Cr2 O3 and CoOx as H2 and O2 evolution cocatalysts, respectively. Results reveal that the dual cocatalysts greatly extract charges from bulk to surface, while the Rh/Cr2 O3 cocatalyst dramatically restrains the backward reaction, achieving an apparent quantum efficiency (AQE) of 20.2 % for the photocatalytic overall water splitting reaction.

Al–SrTiO3/Au/CdS Z-schemes for the efficient photocatalytic H2 production under visible light

Development of sustainable solar fuels to meet the continued increase in the energy need worldwide is of particular importance. In addition, reducing carbon emissions could be the last hope to solve global challenges such as global warming and climate change. For this endeavor, different Al–SrTiO 3/Au/CdS Z-Scheme samples were developed by changing the weight percentage (wt. %) of gold nanoparticles (Au NPs) and the wt% ratio of Al–SrTiO3 to CdS NPs using post annealing of mixed powders method. The prepared samples were characterized using several physicochemical techniques to reveal their properties, then their photocatalytic H2 evolution performance was evaluated under visible light using photodeposited RhCr2O3 as H2 evolution cocatalyst. Our results showed that, Al–SrTiO3 particles possessed high crystallinity and cubic perovskite phase, Au NPs exhibited face-centered cubic (FCC) structure, and CdS NPs had cubic Zinc Blende phase as confirmed by XRD analysis. Our UV–Vis. diffuse reflectance analysis revealed that all prepared Z-scheme samples obtained a strong absorption in both UV and visible regions. SEM analysis confirmed the cubic morphology of the perovskite Al–SrTiO3 particles which were randomly deposited by Au NPs of relatively smaller size. While CdS NPs showed semi-spherical shape and were conjugated with Al–SrTiO3 directly to form the proposed Z-Schemes as proposed by our STEM mapping analysis. The highest amount of H2 (656.7 μ mole) was evolved by Al–SrTiO3/4 wt% Au/CdS (1:1) Z-scheme sample after 3 h of visible light irradiation. This sample had 4 wt % of Au NPs and equimolar ratio of Al–SrTiO3 and CdS NPs. This relatively higher activity might be because of the efficient light absorption, prolonged lifetime of the photogenerated charge carriers and improved charge separation as revealed by the PL analysis. Our study can promote the ongoing efforts toward more carbon neutral societies.

In situ self-exsolved ultrasmall Fe2P quantum dots from attapulgite nanofibers as superior cocatalysts for solar hydrogen evolution.

Developing highly active, stable, and cost-efficient cocatalysts for photocatalytic H2 evolution is pivotal in the area of renewable energy conversion. Herein, we present a straightforward, low-temperature phosphidation strategy for in situ exsolving doped Fe ions from natural attapulgite (ATP) nanofibers into a supported Fe2P cocatalyst for the photocatalytic H2 evolution reaction (HER). The resulting Fe2P QDs/ATP features highly dispersed Fe2P QDs with an average size of <2 nm and a strong interfacial interaction between self-exsolved Fe2P QDs and the ATP substrate, thus providing ample and stable active sites for the photocatalytic HER. When employed as a cocatalyst, Fe2P QDs/ATP exhibits superior catalytic activity and notable stability in a molecular system with low-cost xanthene dyes as the photosensitizer under visible light irradiation. More importantly, Fe2P QDs/ATP can also efficiently and stably catalyze the photocatalytic HER when simply combined with various semiconductor photocatalysts (g-C3N4, TiO2, and CdS). This strategy of exsolving transition metal ions from substrates is an effective yet simple approach for the development of highly active supported HER cocatalysts for renewable and clean energy conversion.

A new, efficient and durable MoO2/Mo2C-C cocatalyst with the optimized composition and electronic structure via in-situ carburization for photocatalytic H2 evolution

Cocatalyst assisted photocatalytic H2 generation from water under mild conditions can meet the increasing demand for clean and sustainable energy, but efficient and super-stable photocatalyst has rarely been achieved by modulating the composition and structure of cocatalyst. Herein, a fantastic cocatalyst, MoO2/Mo2C nanoparticles strongly anchored in conductive carbon matrix (MoO2/Mo2C-C), was accurately synthesized by in-situ carbonizing strategy and adopted as an efficient and robust cocatalyst for CdS photocatalytic H2 evolution. To our delight, the obtained MoO2/Mo2C-C cocatalyst is extremely stable, retaining the original activity even after two years storage in atmospheric conditions. The optimized MoO2/Mo2C-C-CdS-0.3 (MMCC-0.3) photocatalyst, coupling 30 wt% MoO2/Mo2C-C with CdS, delivers a substantial H2 evolution rate of 18.43 mmol h−1 g−1 and super stability of successive 90 h testing (conducted in 15-day) without a secondary sacrificial agent supplement, as well as a high apparent quantum efficiency of 14.13 %. Both experimental results and DFT calculations reveal that the unique MoO2/Mo2C-C cocatalyst not only merited with optimal hydrogen binding energy (ΔG*) and downshifted d-band center to lower the kinetic barrier of hydrogen evolution reaction, but also promise conductive carbon bridge, high quality interface, and exposed abundant active sites for CdS, which synergistically work with enhanced visible light absorption and promoted charge separation to promise the outstanding activity and stability of MoO2/Mo2C-C-CdS photocatalyst. This work not only provides an efficient and low cost cocatalyst for practical application, but also offers valuable insights into the design of robust cocatalyst for photocatalyst and beyond.

Partial Sulphidation to Regulate Coordination Structure of Single Nickel Atoms on Graphitic Carbon Nitride for Efficient Solar H2 Evolution.

To develop a non-precious highly efficient cocatalyst to replace Pt on graphitic carbon nitride (g-C3 N4 ) for solar H2 production is great significant, but still remains a huge challenge. The emerging single-atom catalyst presents a promising strategy for developing highly efficient non-precious cocatalyst owing to its unique adjustability of local coordination environment and electronic structure. Herein, this work presents a facile approach to achieve single Ni sites (Ni1 -N2 S) with unique local coordination structure featuring one Ni atom coordinated with two nitrogen atoms and one sulfur atom, confirmed by high-angle annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, and density functional theory calculation. Thanks to the unique electron structure of Ni1 -N2 S sites, the 1095µmol g-1 h-1 of high H2 evolution rate with 4.1% of apparent quantum yield at 420nm are achieved. This work paves a pathway for designing a highly efficient non-precious transition metal cocatalyst for photocatalytic H2 evolution.

Facile Synthesis of Amorphous NiO/Reduced Graphene Oxide as a Cocatalyst for Enhanced Dye-Sensitized Photocatalytic H2 Evolution

It is still a challenge to develop efficient catalysts for hydrogen evolution reaction (HER) via a low-cost and simple method. Herein, we report an amorphous NiO/reduced graphene oxide (A-NG) composite as a cocatalyst for enhanced photocatalytic H2 evolution via dye sensitization. The A-NG composite is facilely fabricated by calcinating the NiCl2/GO precursor at a low temperature of 250 °C. The detailed characterizations show that amorphous NiO presents as tiny nanoparticles highly dispersed on graphene sheets, and nickel carbide is formed at the NiO/graphene interface, which demonstrates the strong interaction between Ni and the defective carbon of graphene. Compared with crystalline NiO/rGO (C-NG), the A-NG cocatalyst shows much enhanced dye-sensitized photocatalytic HER activity because the amorphous NiO nanoparticles can effectively adsorb the dye. As a result, highly dispersed amorphous NiO accelerates the photoinduced electron transfer from the excited dye to the cocatalyst, namely, the amorphous nickel carbide formed between NiO and rGO. This work provides a low-cost and simple method to develop efficient cocatalysts for photocatalytic H2 evolution.