H2 Evolution Catalyst Research Articles

Heterogenization of a [NiFe] Hydrogenase Mimic through Simple and Efficient Encapsulation into a Mesoporous MOF.

In the quest for new, efficient, and noble-metal-free H2-evolution catalysts, hydrogenase enzymes are a source of inspiration. Here, we describe the development of a new hybrid material based on a structural and functional [NiFe]-hydrogenase model complex (NiFe) incorporated into the Zr-based MOF PCN-777. The bulk NiFe@PCN-777 material was synthesized by simple encapsulation. Characterization by solid-state NMR and IR spectroscopy, SEM-EDX, ICP-OES, and gas adsorption confirmed the inclusion of the guest. FTO-supported thin films of the NiFe@PCN-777 composite were obtained by electrophoretic deposition of the bulk material and characterized by SEM-EDX, ICP-OES, and cyclic voltammetry. The average surface concentration of electroactive NiFe catalyst in the film was found to be ∼9.6 × 10-10 mol cm-2, implying that a surprisingly high fraction (37%) of NiFe units incorporated in the MOF are electroactive. By cyclic voltammetry, we showed that NiFe maintains its electrocatalytic capabilities for H+ reduction inside the MOF cavities, even if under controlled-potential electrolysis conditions the activity of NiFe cannot be discerned from that of free PCN-777 and FTO.

Photochemical H2 Evolution Catalyzed by Porphyrin-based Cubic Cages Singly and Doubly Encapsulating PtCl2(4,4′-dimethyl-2,2′-bipyridine)

A porphyrin-based cubic cage (Cube) was reacted with a Pt(II)-based molecular H2-evolving catalyst, PtCl2(dmbpy) (PtDmb; dmbpy: 4,4′-dimethyl-2,2′-bipyridine), to give Cubes incorporated with one o...

EPR interpretation and electrocatalytic H2 evolution study of bis(3,5-di-methylpyrazol-1-yl)acetate anchored Cu(II) and Mn(II) complexes

Two mononuclear Cu(II) and Mn(II) complexes, [Cu(bdmpza)2] (1) and [Mn(bdmpza)2] (2) (Počkaj et al. 2015 [1]) are afforded by employing a ‘scorpionate’ type precursor [bdmpza=bis(3,5-di-methylpyrazol-1-yl)acetate]. In complex 1, the central Cu(II) atom is surrounded by four Npyrazol atoms from two units of bis(pyrazol-1-yl)acetate and the axial position is occupied by Oacetate atom, thus exhibiting a square-pyramidal geometry with N4O coordination environment. Both the complexes, 1 and 2 are thoroughly characterized by IR and UV–vis spectroscopy. Detailed temperature and solvent dependent EPR spectra for both complexes 1 and 2 are also carried out to get a profoundly insight on magnetic coupling. For the solid complex 1 a structural variation by lowering the temperature and a change in the EPR signals from a S=½ to a S=1 state, in which two Cu(II) magnetically interact, is observed. In organic solution an equilibrium between the penta-coordinated with only one axial COO− group and the hexa-coordinated with two axial COO− groups is revealed for compound 1, whereas 2 maintains the octahedral structure. The highly activity for H2 evolution from proton reduction of complex 1 is reported here. Based on electrochemical investigations (cyclic voltammetry, linear sweep voltammetry, and bulk electrolysis) and gas chromatography experiment, complex 1 afforded an observed rate constant (kobs or TOF) [TOF=Turnover number] value about 2900s−1, 2nd order catalytic rate constant of 9.7×104M−1s−1 and an onset potential 0.5V less negative than blank TFA [Trifluoroacetic acid] solution without 1. Hence, high rate of H2 evolution using this cheap and earth abundant Cu complex demonstrates a promising strategy to design a potential heterogeneous catalyst for H2 evolution from water splitting under electrochemical or by photocatalysis.

Insight into the origin of the limited activity and stability of p-Cu2O films in photoelectrochemical proton reduction

The origin of instability of p-Cu2O films deposited on a platinized Si substrate when used as photocathode in photoelectrochemical water splitting, was studied in the absence or presence of a protective layer of RuO2. When applied at +0.3V vs. RHE and at pH 7, p-Cu2O films were found to show a slightly more stable performance as compared to photoelectrochemical measurements reported in the literature at 0V vs. RHE and under acidic conditions. In addition, the stability and the photocurrent induced by the Cu2O films were significantly improved when H2O2 was added to the electrolyte, which is explained by efficient scavenging of electrons, yielding oxygen and water as confirmed by gas chromatography (GC). Also, other electron acceptors improved the photocatalytic performance of the p-Cu2O films, demonstrating that the transfer of photo-excited electrons to protons adsorbed on the surface is the rate determining step in p-Cu2O based photo-electrochemical water splitting. We confirmed that deposition of RuO2 improves the stability of the films, but to the expense of a decrease in photocurrent density. The results provided in this study rationalize the attachment of an effective H2 evolution catalyst as a means to significantly improve the stability of p-Cu2O electrodes.

Bio-inspired assembly of cubane-adjustable polyoxometalate-based high-nuclear nickel clusters for visible light-driven hydrogen evolution

By artificial mimic of the natural [FeFe]-hydrogenases, a series of polyoxometalate-based high-nuclear Ni clusters containing a varying number of {Ni4O4} cubane cores, K1.5Na26.5[{Ni4(OH)3(PO4)}4(A-PW9O34)4]·62H2O (1), Na28[{Ni4(OH)3(PO4)}4(A-PW9O34)2(B-PW9O34)2]·102H2O (2), and Na28[{Ni4(OH)3(VO4)}4(B-PW9O34)4]·74H2O (3), were synthesized and systematically characterized. Compounds 1−3 contain {Ni16(XO4)4(OH)12} (X=P,V) core encapsulated by the trivacant A-/B-{PW9O34} ligands. Compounds 1−3 as homogeneous catalysts for visible-light-driven H2 evolution indicate that they not only show high photocatalytic performance (High TON of 578.8, 679.1, and 931.1 for 1−3 were achieved, respectively), but also their catalytic performance was improved with the increasing number of {Ni4O4} cubanes. Multiple stability experiments confirm that compounds 1−3 maintain their structure intact under the photocatalytic conditions. The above research provides a platform for mimicking the structures of natural hydrogenases to further explore more efficient and inexpensive H2 evolution catalysts.

Designing Highly Efficient CuI Photosensitizers for Photocatalytic H2 Evolution from Water.

A series of CuI photosensitizers was synthesized, characterized, and investigated for photocatalytic H2 evolution from water. A structure-property correlation was established for their catalytic activity and photophysical properties, which was further elaborated by DFT calculations. A new CuI photosensitizer (Cu-TPAPhen) with triphenylamine-substituted phenanthroline ligands showed unprecedentedly high turnover numbers of 19 000 when tested in combination with triethylamine as a sacrificial reagent and colloidal Pt as a H2 evolution catalyst. This work paves the way toward cheap metal-based photosensitizers which can replace noble-metal complexes in photocatalytic systems.

In-situ photochemical fabrication of transition metal-promoted amorphous molybdenum sulfide catalysts for enhanced photosensitized hydrogen evolution

Amorphous molybdenum sulfide catalysts (MoSx) can efficiently catalyze the H2 evolution reaction (HER); however, their catalytic activities are still limited that need to be improved. Herein, transition metal-promoted MoSx H2 evolution catalysts were facilely fabricated through an in-situ photochemical reduction with inexpensive organic dye as photosensitizers. Under visible light (λ ≥ 420 nm), the promotional effect of transition metals on the H2 evolution over MoSx follows the order of Co > Fe ≈ Ni > unpromoted > Cu > Zn in Erythrosin B-triethanolamine (ErB-TEOA) system. The most active Co-promoted MoSx (Co-MoSx) catalyst is amorphous and composed of inter-connected nanoparticles with diameters of 30–50 nm. The Co-MoSx catalyst contains both CoMoS phase and Co oxides/hydroxides. At the optimal reaction conditions, the Co-MoSx catalyst with Co:Mo ratio of 4:6 exhibits enhanced H2 evolution activity by 2 times as compared to unpromoted MoSx and turnover numbers (TONs) of 30 and 60 based on ErB and catalyst used, respectively. The Co-MoSx catalyst also shows a long-term stability without noticeable activity degradation. The formation pathways of Co-MoSx catalyst and the photocatalytic mechanism for enhanced H2 evolution performance were studied and a two-step reaction mechanism involved an oxidative quenching pathway of dye was proposed. This study demonstrates that in-situ concurrent photochemical fabrication with transition metal modification of amorphous MoSx catalyst is an effective strategy for development of MoSx-based HER catalysts with enhanced performances.

Synthesis of bio-inspired mononuclear nickel hydrogen production catalysts and photocatalytic efficiency improvement with porphyrin covalently functionalized graphene nanohybrid

Eight nickel complexes with chelating N-substituted bis(diphenylphosphanyl)amine and 1,2-benzenedithiolate or 3,4-toluenedithiolate, [RN(PPh2)2]Ni(1,2-SC6H4S) [R=CH(CH3)2, 1; CH2CH(CH3)2, 2; CH2CH2CH2CH3, 3; CH2Ph, 4] and [RN(PPh2)2]Ni[3,4-SC6H3(CH3)S] [R=CH(CH3)2, 5; CH2CH(CH3)2, 6; CH2CH2CH2CH3, 7; CH2Ph, 8], were synthesized and structurally characterized. The measurement of the electrochemical properties revealed that complex 4 can catalyze protons to hydrogen (H2) under weak acidic conditions. Complex 4 can also be used as a molecular catalyst for light-driven H2 evolution with a proton source, a photosensitizer, and an electron donor. Furthermore, by using tetraphenylporphyrin (TPP) amide-covalently functionalized graphene oxide (GO) nanohybrid (TPP-NH-GO) as a photosensitizer, the efficiency of photocatalytic H2 production of complex 4 in aqueous ethanol solution had been astonishingly improved over than for the photocatalytic systems without GO. This result suggests that the excellent properties of GO with respect to electron transfer, surface area, adsorptivity, and hydrophilicity may promote the performance of the photocatalytic H2 production system to a certain extent.

Coordination Chemistry and Reactivity of Bis(aldimino)pyridine Nickel Complexes in Four Different Oxidation States

A series of nickel complexes with potentially redox active bis(aldimino)pyridine ligands [NNN] ([NNN] = 1,1′-(pyridine-2,6-diyl)bis(N-arylmethanimine), where aryl = 2,6-diisopropylphenyl, mesityl, 4-methoxyphenyl, 4-trifluoromethylphenyl, and 3,5-bis(trifluoromethyl)phenyl) were synthesized, and their properties and reactivities were investigated as a function of the overall oxidation state of the system. (Ni[NNN])2+ complexes of ligands featuring bulky electron-rich substituents (1a-Br2 and 1b-Br2, [NNN] = 1,1′-(pyridine-2,6-diyl)bis(N-(2,6-diisopropylphenyl)methanimine) and 1,1′-(pyridine-2,6-diyl)bis(N-mesitylmethanimine), respectively) demonstrated five electrochemical reduction events, the first three of which were quasi-reversible. In contrast, only two quasi-reversible reductions were observed for the less bulky and electron-deficient N-aryl substituents 4-(trifluoromethyl)phenyl and 3,5-bis(trifluoromethyl)phenyl. Chemical reduction of 1a-Br2 and 1b-Br2 with 1 equiv of KC8 or CoCp*2 forms (Ni[NNN])+ complexes of the general formula Ni[NNN]Br (2a-Br and 2b-Br). Structural, spectroscopic, and theoretical studies reveal that these complexes feature significant unpaired spin density on the metal, consistent with “nickel(I)” character. This behavior is in contrast with previously reported bis(ketimino)pyridine systems, in which at the (Ni[NNN])+ state the unpaired electron resided exclusively in the ligand. Further reduction forms a series of (Ni[NNN])0 complexes, in which all of the potentially tridentate [NNN] ligands bind via only one iminopyridine unit; the second arm is left unbound in most complexes. Variable temperature NMR spectroscopy demonstrates that bound and unbound arms exchange via a postulated tridentate intermediate. Electrochemical reduction, via three sequential one-electron reductions, of 1a-Br2 and 1b-Br2 in the presence of CO2/H+ forms an active catalyst for H2 evolution at a glassy-carbon electrode surface, again emphasizing the unique redox chemistry of the bulky bis(aldimino)pyridine nickel complexes.

Graphitic C3N4 modified by Ni2P cocatalyst: An efficient, robust and low cost photocatalyst for visible-light-driven H2 evolution from water

The development of an efficient, robust and low cost catalyst for photocatalytic H2 evolution is an uphill challenge and has attracted plenty of researchers’ interest. Herein, we report g-C3N4/Ni2P composite photocatalyst for H2 evolution reaction in which Ni2P acts as a noble-metal-free cocatalyst for g-C3N4. The g-C3N4/Ni2P is prepared based on two-step hydrothermal and phosphidation method. The optimum H2 evolution ability is obtained when the loaded weight percent of Ni2P is 0.48% (g-C3N4/Ni2P-0.48%), along with a corresponding H2 evolution rate of 5.67μmolh−1. This value is about 1418 times more than pure g-C3N4 and obviously higher than that of Pt modified g-C3N4 (3.78μmolh−1). In addition, the g-C3N4/Ni2P-0.48% catalyst demonstrates almost negligible photocatalytic degradation capability even after eight repeated cycles (a reaction time of 12h per cycle). The introduction of Ni2P cocatalyst significantly accelerates the separation and transfer of photogenerated electrons of g-C3N4, hence resulting in enhanced H2 evolution efficiency. In addition, the Ni and P in Ni2P cocatalyst act as the hydride-acceptor and proton-acceptor centers, respectively, which synergistically facilitate the fast generation of H2.

Solar H2 evolution in water with modified diketopyrrolopyrrole dyes immobilised on molecular Co and Ni catalyst-TiO2 hybrids.

A series of diketopyrrolopyrrole (DPP) dyes with a terminal phosphonic acid group for attachment to metal oxide surfaces were synthesised and the effect of side chain modification on their properties investigated. The organic photosensitisers feature strong visible light absorption (λ = 400 to 575 nm) and electrochemical and fluorescence studies revealed that the excited state of all dyes provides sufficient driving force for electron injection into the TiO2 conduction band. The performance of the DPP chromophores attached to TiO2 nanoparticles for photocatalytic H2 evolution with co-immobilised molecular Co and Ni catalysts was subsequently studied, resulting in solar fuel generation with a dye-sensitised semiconductor nanoparticle system suspended in water without precious metal components. The performance of the DPP dyes in photocatalysis did not only depend on electronic parameters, but also on properties of the side chain such as polarity, steric hinderance and hydrophobicity as well as the specific experimental conditions and the nature of the sacrificial electron donor. In an aqueous pH 4.5 ascorbic acid solution with a phosphonated DuBois-type Ni catalyst, a DPP-based turnover number (TONDPP) of up to 205 was obtained during UV-free simulated solar light irradiation (100 mW cm-2, AM 1.5G, λ > 420 nm) after 1 day. DPP-sensitised TiO2 nanoparticles were also successfully used in combination with a hydrogenase or platinum instead of the synthetic H2 evolution catalysts and the platinum-based system achieved a TONDPP of up to 2660, which significantly outperforms an analogous system using a phosphonated Ru tris(bipyridine) dye (TONRu = 431). Finally, transient absorption spectroscopy was performed to study interfacial recombination and dye regeneration kinetics revealing that the different performances of the DPP dyes are most likely dictated by the different regeneration efficiencies of the oxidised chromophores.

Serial microbubble imaging technology (sMBI) for rapid screening of hydrogen-evolution materials used in photocatalytic water-splitting reactions

A new detection method, serial microbubble imaging (sMBI) was developed for high-throughput screening of thousands of H2-evolution catalysts.

Synthesis and Characterization of 0D-3D Copper-Containing Tungstobismuthates Obtained from the Lacunary Precursor Na9[B-α-BiW9O33

The reaction of the lacunary polyoxometalate precursor Na9[B-α-BiW9O33]·19.5H2O with Cu(II) ions was explored in search of new economic ways to copper tungstobismuthates as interesting prototypes for water oxidation and reduction catalysts. The emerging series of new 0D-3D polyoxometalate architectures with distinct copper cores was structurally characterized. Na6Rb6[Cu3(H2O)3(BiW9O33)2] (Cu-4) and 3D-K6.56Cu0.43H2.20[(Cu3Cl)(K2.62Cu0.38(H2O)3)(B-α-BiW9O33)2]·13H2O (Cu-5) display a Cu3(H2O)3 core. The 2D representatives Na12[Cu2(H2O)4Cl2(BiW10O35)2] (Cu-1a), Na10[Cu2(H2O)6(BiW10O35)2] (Cu-1b), 2D-Na7K3Cu0.5Cl[Cu2(H2O)4(BiW10O35)2] (Cu-2), and 2D-Na5.5K2.5Cu[Cu2(H2O)4(BiW10O35)2] (Cu-3) contain Cu2(H2O)nW2O4 cores. Interestingly, the bismuth-free 1D paratungstate B Na4K4Cu[H2W12O42] (Cu-6) is formed through reassembly of the precursor. Cu-5 displays a disordered transition metal core, implying the presence of the polyanions [Cu4(H2O)4(BiW9O33)2]10- and [Cu5(H2O)5(BiW9O33)2]8-. The magnetic properties of Cu-5 as well as its activity as visible-light-driven H2 and O2 evolution catalyst were evaluated.

CoSe2 Embedded in C3N4: An Efficient Photocathode for Photoelectrochemical Water Splitting.

An efficient H2 evolution catalyst is developed by grafting CoSe2 nanorods into C3N4 nanosheets. The as-obtained C3N4-CoSe2 heterostructure can show excellent performance in H2 evolution with outstanding durability. To generate phatocathode for photoelectrochemical water splitting CoSe2 grafted in C3N4 was decorated on the top of p-Si microwires (MWs). p-Si/C3N4-CoSe2 heterostructure can work as an efficient photocathode material for solar H2 production in PEC water splitting. In 0.5 M H2SO4, p-Si/C3N4-CoSe2 can afford photocurrent density -4.89 mA/cm2 at "0" V vs RHE and it can efficiently work for 3.5 h under visible light. Superior activity of C3N4-CoSe2 compared to CoSe2 toward H2 evolution is explained with the help of impedance spectroscopy.

Molybdenum carbide microcrystals: Efficient and stable catalyst for photocatalytic H2 evolution from water in the presence of dye sensitizer

Rod-like molybdenum carbide (Mo2C) microcrystals were obtained from the pyrolysis of Mo-containing organic-inorganic hybrid composite. We investigated the photocatalytic H2 evolution activity of Mo2C by constructing a Mo2C-dye sensitizer photocatalyst system. A high quantum efficiency of 29.7% was obtained at 480 nm. Moreover, Mo2C catalyst can be easily recycled by simple filtration.

Solar-Driven Reduction of Aqueous Protons Coupled to Selective Alcohol Oxidation with a Carbon Nitride-Molecular Ni Catalyst System.

Solar water-splitting represents an important strategy toward production of the storable and renewable fuel hydrogen. The water oxidation half-reaction typically proceeds with poor efficiency and produces the unprofitable and often damaging product, O2. Herein, we demonstrate an alternative approach and couple solar H2 generation with value-added organic substrate oxidation. Solar irradiation of a cyanamide surface-functionalized melon-type carbon nitride (NCNCNx) and a molecular nickel(II) bis(diphosphine) H2-evolution catalyst (NiP) enabled the production of H2 with concomitant selective oxidation of benzylic alcohols to aldehydes in high yield under purely aqueous conditions, at room temperature and ambient pressure. This one-pot system maintained its activity over 24 h, generating products in 1:1 stoichiometry, separated in the gas and solution phases. The NCNCNx–NiP system showed an activity of 763 μmol (g CNx)−1 h–1 toward H2 and aldehyde production, a Ni-based turnover frequency of 76 h–1, and an external quantum efficiency of 15% (λ = 360 ± 10 nm). This precious metal-free and nontoxic photocatalytic system displays better performance than an analogous system containing platinum instead of NiP. Transient absorption spectroscopy revealed that the photoactivity of NCNCNx is due to efficient substrate oxidation of the material, which outweighs possible charge recombination compared to the nonfunctionalized melon-type carbon nitride. Photoexcited NCNCNx in the presence of an organic substrate can accumulate ultralong-lived “trapped electrons”, which allow for fuel generation in the dark. The artificial photosynthetic system thereby catalyzes a closed redox cycle showing 100% atom economy and generates two value-added products, a solar chemical, and solar fuel.

Self-Healing of Molecular Catalyst and Photosensitizer on Metal–Organic Framework: Robust Molecular System for Photocatalytic H2 Evolution from Water

Inspired by self-repair mechanism of PSII in plants, we report a self-healing system which spontaneously repairs molecular catalyst and photosensitizer during photocatalytic H2 evolution. A bipyridine-embedded UiO-type metal-organic framework (MOF), namely Ptn_Ir_BUiO, which incorporated H2-evolving catalyst and photosensitizer, was synthesized and subject to photocatalytic H2 evolution reaction (HER). Impressively, HER with Pt0.1_Ir_BUiO showed very stable molecular photocatalysis without significant decrease in its activity and colloidal formation for 6.5 days at least; in the homogeneous counterpart, the molecular catalyst became a colloid just after 7.5 h. It was revealed that the arrangement of diimine sites which closely and densely surrounded the H2-evolving catalyst and photosensitizer in the MOF enabled such a highly efficient self-healing.

Beyond Metal-Hydrides: Non-Transition-Metal and Metal-Free Ligand-Centered Electrocatalytic Hydrogen Evolution and Hydrogen Oxidation.

A new pathway for homogeneous electrocatalytic H2 evolution and H2 oxidation has been developed using a redox active thiosemicarbazone and its zinc complex as seminal metal-free and transition-metal-free examples. Diacetyl-bis(N-4-methyl-3-thiosemicarbazone) and zinc diacetyl-bis(N-4-methyl-3-thiosemicarbazide) display the highest reported TOFs of any homogeneous ligand-centered H2 evolution catalyst, 1320 and 1170 s(-1), respectively, while the zinc complex also displays one of the highest reported TOF values for H2 oxidation, 72 s(-1), of any homogeneous catalyst. Catalysis proceeds via ligand-centered proton-transfer and electron-transfer events while avoiding traditional metal-hydride intermediates. The unique mechanism is consistent with electrochemical results and is further supported by density functional theory. The results identify a new direction for the design of electrocatalysts for H2 evolution and H2 oxidation that are not reliant on metal-hydride intermediates.

An effective preparation method of composite photocatalysts for hydrogen evolution using an organic photosensitizer and metal particles assembled on alumina-silica

Composite catalysts for photocatalytic hydrogen (H2) evolution were prepared by loading an organic electron donor–acceptor linked dyad [2-phenyl-4-(1-naphthyl)quinolinium ion, QuPh+–NA] as an organic photosensitizer and Pt or Cu particles as H2-evolution catalysts on alumina-silica. The composite catalysts loading Pt particles were prepared by two different methods; first, Pt particles were deposited by reduction of PtCl62− owing to photocatalysis of QuPh+–NA supported on alumina-silica (PD method), and second, alumina-silica was impregnated with the PtCl62− and calcined, and then QuPh+–NA was loaded on the Pt/alumina-silica by a cation exchange method (IMP method). When a composite catalyst was prepared by the IMP method, a high Pt-loading amount of 4.2wt% was necessary to achieve the highest H2-evolution rate of 0.27μmolh−1. On the other hand, a composite catalyst prepared by the PD method exhibited three times faster H2 evolution (0.83μmolh−1) even though the loading amount of Pt was as low as 0.4wt%. The activity of composite catalysts prepared by the PD method highly depends on the electric charges of precursors for Pt particles. A composite catalyst prepared with positively charged Pt(NH3)42+ as a precursor of Pt particles exhibited low catalytic activity with the H2-evolution rate of 0.10μmolh−1, which is significantly lower than the rate (0.27μmolh−1) for the composite catalyst prepared with PtCl62−. However, such precursor-dependence was not observed for composite catalysts employing Cu particles as an H2-evolution catalyst, because the Cu precursors are more labile than the Pt precursors in a reaction solution. The electrostatic interaction between the precursors of metal particles and negatively charged surfaces of alumina-silica should be taken into account to construct efficient H2-evolution catalysts.

Periodic polarity reversal for stabilizing the pH in two-chamber microbial electrolysis cells

A successful pH control is of critical importance for ensuring efficient H2 production in two-chamber MECs. In this study, a novel two-chamber MEC is developed with biotic/abiotic hybrid electrodes, which are composed of carbon felt (CF) and stainless steel (SS) mesh. The CF is used for the electrogenic microorganisms attachment catalyzing the oxidation of organic matter (OM); the SS serves as the current collector and the H2 evolution catalyst. The MEC is operated in the periodic polarity reversal (PPR) mode and two hybrid electrodes work alternately as an anode and a cathode. With the hybrid electrodes and the PPR mode, the pH fluctuation is limited within the range of 6.4–8.6, and the H2 production is 5.3 times that of control without the PPR mode. The optimal reversal interval is 2h for maximal H2 production. The H2 production increases with the amplitude of the applied voltage (0.7–1.0V). The using of hybrid electrodes, combining with the PPR mode, provides a simple but efficient pH control strategy and better H2 production performance in MECs. The findings of this study are expected to facilitate the design of pilot-scale MECs or similar bio-electrochemical reactors in future research.