Shift Of Onset Potential Research Articles

Improving electrocatalytic performance of Ni-based catalysts: fuel blend strategy and DFT calculations

This study addresses the electrooxidation behavior of glycerol/glucose (as a fuel blend) at commercial carbon fibers decorated with NiOxHy nanostructures. Blending glycerol with various ratios of glucose results in better fuel utilization (FU) together with a higher turnover number (TON). For instance, using an equimolar (1:1) fuel blend exhibits the highest performance compared to pure fuels (glucose or glycerol) as demonstrated by the oxidation current and negative shift of onset potential, besides a 2-fold improvement of FU and TON at 0.6V. DFT calculations guided the reason behind the observed enhancement to the favorable change of the glucose adsorption mode in the presence of glycerol via hydrogen bonding between glucose and glycerol. The formed hydrogen bonds assist in the elongation of the O-H bond at which oxidation is most likely to occur between (O11 and H12) in glycerol from 0.99 Å in pure to 1.06 Å for glycerol/glucose blend. Also, a positive shift of HOMO orbital energy, lower ionization energy for (+2 cation), and more negative energy value are estimated to reflect a higher ability of the blend to form and to donate electrons to the underlying catalyst.

Computational fluid dynamics simulation of bubble hydrodynamics in water splitting: Effect of electrolyte inflow velocity and electrode morphology on cell performance

Efficient management of oxygen gas bubbles evolving at the photoanode is important for a good overall performance of a photoelectrochemical (PEC) cell. The process of formation, detachment, coalescence and rise affects the bubble residence time at or near the photoanode. A reduced bubble residence time promotes easier electrolyte access to the photoanode surface, thereby enhancing the oxygen evolution reaction (OER) kinetics. In this work, computational fluid dynamics (CFD) simulations using laminar flow and phase-field model in COMSOL Multiphysics are conducted to study the gas bubble hydrodynamics for different bubble configurations, sizes, and bubble gaps. CFD results predict enhanced bubble rise in the presence of forced convection, i.e., some electrolyte inflow velocity (u≠0m.s−1). Experimental results using hematite as the model electrode also show a higher photocurrent density (ca. 4.33 mA.cm−2 at 2 V vs. RHE) for u = 0.1 m.s−1, compared to that without flow (3.5 mA.cm−2 at 2 V vs. RHE). This indicates improved access of electrolyte at the electrode surface and faster OER. Further, CFD simulations for electrode morphology effects show a reduced bubble adhesion for hydrophilic hematite nanorod arrays compared to planar photoanode, due to capillary wicking. The continuous contact film detaches and results in a reduced blockage of active sites at the bubble base, thereby enhancing the PEC performance for the nanorod arrayed morphology. Here too, experimental results show a four-fold increase in photocurrent density (ca. 0.1 mA.cm−2 at 1.5 V vs. RHE) and a 210 mV cathodic shift in onset potential for nanorods, compared to planar electrodes (0.025 mA.cm−2 at 1.5 V vs. RHE). A significant reduction in charge transfer resistance is observed for the former, implying better OER kinetics. The results obtained help in the understanding of transient processes involving O2 bubble hydrodynamics and electrolyte usage efficiency in a PEC reactor.

Self‐Supporting and Shell‐Core Pd−Ni@Ni Nanowire Arrays Electrode as Anode of Direct Carbohydrazide Fuel Cell

AbstractConsidering the excessively high onset potential on pure Ni catalyst and the generation of gaseous products in carbohydrazide (CHZ) electrooxidation, a self‐supporting and shell‐core Pd−Ni@Ni nanowire arrays (NAs) catalytic electrode is prepared by the first templating electrodeposition of Ni and the subsequent galvanic replacement of Pd. The introduction of Pd with minute mass loadings of 2.7–5.3 μg cm−2 enables a negative shift of onset potential of CHZ electrooxidation by 320 mV regardless of Ni supports. Pd in Ni@Pd−Ni NAs electrode can facilitate the chemical dissociation of CHZ into N2H4 and/or H2 and then provoke the occurrence of side reactions, i. e., N2H4 and/or H2 electrooxidation. The direct CHZ fuel cell made of Ni@Pd−Ni NAs anode delivers an open circuit voltage of 1.05 V and a peak power density of 22.90 mV cm−2 at the operating temperature of 303 K.

Photochemically Etching BiVO4 to Construct Asymmetric Heterojunction of BiVO4 /BiOx Showing Efficient Photoelectrochemical Water Splitting.

BiVO4 as a promising semiconductor candidate of the photoanode for solar driven water oxidation always suffers from poor charge carrier transport property and photo-induced self-corrosion. Herein, by intentionally taking advantage of the photo-induced self-corrosion process, a controllable photochemical etching method is developed to rationally construct a photoanode of BiVO4 /BiOx asymmetric heterojunction from faceted BiVO4 crystal arrays. Compared with the BiVO4 photoanode, the resulting BiVO4 /BiOx photoanode gains over three times enhancement in short-circuit photocurrent density (≈3.2mAcm-2 ) and ≈75mV negative shift of photocurrent onset potential. This is due to the formation of the strong interacted homologous heterojunction, which promotes photo-carrier separation and enlarges photovoltage across the interface. Remarkably, the photocurrent density can remain at ≈2.0mAcm-2 even after 12h consecutive operation, while only ≈0.1mAcm-2 is left for the control photoanode of BiVO4 . Moreover, the Faraday efficiency for water splitting is determined to be nearly 100% for the BiVO4 /BiOx photoanode. The controllable photochemical etching process may shed light on the construction of homologous heterojunction on other photoelectrode materials that have similar properties to BiVO4 .

Boosted formic acid electro-oxidation on platinum nanoparticles and "mixed-valence" iron and nickel oxides.

The modification of Pt nanoparticles (nano-Pt, assembled electrochemically onto a glassy carbon (GC) substrate) with hybrid multivalent nickel (nano-NiOx) and iron (nano-FeOx) oxide nanostructures was intended to steer the mechanism of the formic acid electro-oxidation (FAO) in the desirable dehydrogenation pathway. This binary modification with inexpensive oxides succeeded in mediating the reaction mechanism of FAO by boosting reaction kinetics "electron transfer" and amending the surface geometry of the catalyst against poisoning. The sequence of deposition was optimized where the a-FeOx/NiOx/Pt/GC catalyst (where "a" denotes a post-activation step for the catalyst at -0.5 V in 0.5 mol L-1 NaOH) reserved the best hierarchy. Morphologically, while nano-Pt appeared to be spherical (ca. 100 nm in average diameter), nano-NiOx appeared as flowered nanoaggregates (ca. 56 nm in average diameter) and nano-FeOx (after activation) retained a plate-like nanostructure (ca. 38 nm in average diameter and 167 nm in average length). This a-FeOx/NiOx/Pt/GC catalyst demonstrated a remarkable catalytic efficiency (125 mA mgPt-1) for FAO that was ca. 12.5 times that of the pristine Pt/GC catalyst with up to five times improvement in the catalytic tolerance against poisoning and up to -214 mV shift in the FAO's onset potential. Evidences for equipping the a-FeOx/NiOx/Pt/GC catalyst with the least charge transfer resistance and the highest stability among the whole investigated catalysts are provided and discussed.

Hole Storage Interfacial Regulation of Sb2Se3 Photocathode with Significantly Enhanced Photoelectrochemical Performance.

Although interfacial engineering materials for antimony selenide (Sb2Se3) photocathodes have been intensively studied, most of the previous research has focused on the development of photogenerated electron transfer promoters. In this work, Sb2Se3 photocathodes are innovatively modified by using ferrihydrite (Fh), which has been widely used as a hole storage layer in photoanodes. After modifying Fh, the photocurrent density of the Sb2Se3 photocathode was increased from -0.27 to -1.6 mA cm-2 at 0 VRHE with the onset potential positive shift about 150 mV, and an impressive injection efficiency of 83.84% was achieved. The major contribution of Fh to the photoelectrochemical (PEC) performance enhancement was demonstrated by various characterization studies. The results show that the enhancement performance of PEC is largely attributed to the capture of back-migrating holes by Fh, the reduction of interfacial charge transfer resistance, and the significant increase in electrochemical active surface area (ECSA). This work presents new insights into the application of hole storage layers in Sb2Se3-based photocathodes.

Constructing NCuS Interface Chemical Bonds over SnS2 for Efficient Solar-Driven Photoelectrochemical Water Splitting.

The restricted charge transfer and slow oxygen evolution reaction (OER) dynamics tremendously hamper the realistic implementation of SnS2 photoanodes for photoelectrochemical (PEC) water splitting. Here, a novel strategy is developed to construct interfacial NCuS bonds between NC skeletons and SnS2 (CuNC@SnS2 ) for efficient PEC water splitting. Compared with SnS2 , the PEC activity of CuNC@SnS2 photoelectrode is tremendously heightened, obtaining a current density of 3.40 mA cm2 at 1.23 VRHE with a negatively shifted onset potential of 0.04 VRHE , which is 6.54 times higher than that of SnS2 . The detailed experimental characterizations and theoretical calculation demonstrate that the interfacial NCuS bonds enhance the OER kinetic, reduce the surface overpotential, facilitate the separation of photon-generated carriers, and provide a fast transmission channel for electrons. This work presents a new approach for modulating charge transfer by interfacial bond design in heterojunction photoelectrodes toward promoting PEC performance and solar energy application.

Rational Designing of Co–N–C Electrocatalysts for Comprehensive Elucidation of Intrinsic and Extrinsic Activities in the Oxygen Reduction Reaction

The catalytic efficacy of an electrocatalyst is mostly apprised by the intrinsic activity of individual active sites and/or by extrinsic activity, which is dependent on the active site density. In oxygen electrochemistry, extrinsic activity can influence the concomitant current density, while intrinsic activity can potentially influence the onset potential, exchange current density, and half-wave potential besides the current density. Modulation of intrinsic activity is mostly limited as it is mainly dependent on the electronic and chemical structure of active sites. The extrinsic activity can be improved by employing the post-synthesis modifications without disturbing the inherent catalytic nature (i.e., intrinsic activity) of individual active sites to ensure the utility of maximum instituted centers. In this work, we have made an attempt to elucidate the intrinsic and extrinsic activities of Co–N–C-based nanostructures to promote the oxygen reduction reaction (ORR) efficiency, which is further elucidated by X-ray absorption spectroscopic studies. The experimental finding suggests that an increase in the N content (∼9 at %) in the host medium, that is, carbon, decisively impacts the intrinsic nature of electrocatalysts with a positive shift in the ORR onset potential of ∼ 131 mV and a nearly 1.5-fold increase in the exchange current density, a matrix that gives a measure of the ability to support catalytic activity inherently. The targeted removal of electrochemically less effective Co nanoparticles (which block/obscure the active centers Co–Nx in their vicinity) ensures the structural intactness as the C 1s full width at half maximum of the host matrix along with ORR onset potentials and Tafel slopes remains unchanged. The experimental finding further indicates that the current density can be improved by a factor of 2.6 (i.e., from 2.13 to 5.65 mA/cm2), ensuring the effective utilization of electrocatalysts. Overall, the rational combination of intrinsic and extrinsic activities can be valuable to design a variety of transition metal-carbon based electrocatalysts for diverse electrochemical energy devices.

ЕФЕКТИВНИЙ ЕЛЕКТРОКАТАЛІЗАТОР ВИДІЛЕННЯ ВОДНЮ З ВОДИ НА ОСНОВІ ДОПОВАНИХ ВАНАДІЄМ Mo2C, Mo2N ТА ВІДНОВЛЕНОГО ОКСИДУ ГРАФЕНУ

Molybdenum compounds (Mo2C, MoS2, MoP, Mo2N, etc.) and their composites with different nanosized carbon materials are considered to be one of the most promising Pt-free hydrogen evolution reaction (HER) electrocatalysts. Along with non-metallic dopants (N, P etc.), d-metals are also used as dopants to increase the activity of Mo-containing hybrid catalysts in HER. Thus, we have recently shown the possibility of obtaining HER nanocomposite electrocatalysts based on vanadium doped particles of Mo2C and N,P-doped reduced graphene oxide (rGO) using precursor based on polypyrrole, H3PVMo11O40 (PVMo11) and rGO – V-Mo2C/N,P-rGO. It was found that doping with vanadium atoms in situ promotes an increase in the activity of catalysts in HER, compared with the analogue obtained in the absence of V doping. The nature of the nitrogen-containing conjugated polymer can also affect the type of metal-containing particles formed during the high-temperature processing of such macromolecules together with the metal precursors. Given this, the paper shows the possibility of obtaining a promising hybrid electrocatalyst for HER based on vanadium-doped Mo2C, Mo2N and N,P-doped rGO (V-Mo2C,Mo2N/N,P-rGO) by pyrolysis of composite-precursor based on poly-5-aminoindole, PVMo11 and rGO. It was found that the simultaneous presence of Mo2C and Mo2N phases in the catalyst causes an increase in the activity of V-Mo2C,Mo2N/N,P-rGO in HER compared to the analogue containing only Mo2C phase (V-Mo2C/N,P-rGO), which is manifested in reduction in hydrogen evolution overpotential at a current density of 10 mA/cm2 (on 15-29 mV), an increase in the magnitude of exchange currents (by ~ 2.3-2.7 times), as well as in the anodic shift of the process onset potential and the reduction of Tafel slope (in alkaline electrolyte).

A novel synergy of Co/La co-doped porous BiVO4 photoanodes with enhanced photoelectrochemical solar water splitting performance

This work discussed a straightforward approach to manufacture Co-, La-, and Co/La-doped BiVO4 nanoporous films. The effect of doping in the photoelectrochemical (PEC) water splitting performance was evaluated through PEC test and the strong electronic correlation of the framework in the density functional theory (DFT) calculation was taken into account. It was shown that replacing Bi atoms with Co would decrease the bandgap of BiVO4, but doping with La shifted the bandgap from indirect to direct and resulted in the negative shift of onset potential. Furthermore, doping Co and La ions into BiVO4 also introduced deep levels into the BiVO4 bandgap. After the optimization of the mole ration of Co to La, the (0.7/0.3)Co/La:BiVO4 photoanode achieved a high photocurrent density of 3.65 mA cm−2 under the simulated solar irradiation with a bias of 1.23 VRHE, resulting in an H2/O2 production rate of 57.6/25.8 μmol cm−2 h−1. More importantly, without any co-catalysts and hole scavengers, the photoanode presented a favorable stability during 16 h test. The enhanced PEC performance was mainly due to improved visible light absorption and carrier separation ability. Both the experimental and theoretical demonstrations proved that the dual-element doping strategy shed light on designing efficient and stable photoelectrodes for solar energy conversion.

Pt nanoparticles coupled with perylene-based small molecule deposited on Ti3+ self-doped TiO2 nanorods-An inorganic/organic type-II nanoheterostructure for efficient visible-light photoelectrochemical water oxidation.

In the work reported in this article, we have coupled Ti3+-self-doped TiO2 nanorods (NRs) with a newly synthesized tetrathiophene coupled perylene-based molecule (tThTMP) to form type-II inorganic/organic nanoheterostructures (NHs) for visible-light-driven water oxidation. The small organic molecule helps in better utilizing a wide range of the visible light spectrum, facilitates a faster delocalization of the photogenerated carriers at the inorganic/organic heterojunction, and exhibits improved photoelectrochemical performances. We have further decorated the NHs with platinum nanoparticles (NPs). The decoration of the Pt NPs significantly augments the various aspects of photoelectrochemical performances. The Pt NPs decorated NHs photoanode exhibits a photocurrent density of 0.83mA/cm2 at 1.23V vs. RHE (@10mV/s scan rate), a photoconversion efficiency of 0.26%, a substantial cathodic shift in the water oxidation onset potential and flat band potential, impressively reduced charge transfer resistance, improved photocarrier concentration, photovoltage, and stability.

Enhanced and stable photoelectrochemical H2 production using a engineered nano multijunction with Cu2O photocathode

Cuprous oxide (Cu2O) is one of the ideal photocathodes explored for solar water splitting applications due to its suitable optical properties and band edge positions. However, state-of-the-art Cu2O employs Au back contact for hole extraction and Pt or Ru catalyst for water reduction reactions. Moreover, photo-corrosion of Cu2O during the AM 1.5 G illumination is one of the serious challenges that limit the efficiency of water splitting reactions. In this work, a multijunction strategy in which the Cu2O is sandwiched between the stoichiometrically engineered hole extraction layer and an efficient, non-toxic MoOx catalyst layer is proposed for the enhanced charge separation and stable H2 production activity. The optimized multijunction system exhibits the highest photocurrent of 6.1 mA cm−2 at 0 V vs RHE reported for noble metal-free Cu2O photocathodes. Furthermore, a significant anodic shift in onset potential was noticed. In the multijunction, the tuned layers of NiOx, aluminum-doped zinc oxide, and MoOx act as hole scavenger, electron tunneler, and H2 catalyst, respectively. Importantly, the proposed nanolayers multijunction system demonstrates the effective utilization of noble metal and sulfide-free components for stable and enhanced H2 productions employing Cu2O photocathodes.

Bi Doped Sb2S3 Thin Film Synthesized by a Two-Step Approach with Enhanced Photoelectrochemical Water Splitting Performance

Photoelectrochemical water splitting (PEC) is believed as a promising approach to address the energy and environmental crisis. Here, we adopted a simple two-step method to synthesize bare Sb2S3 film, and then employed a Bi element doping strategy to improve the PEC performance of obtained bare Sb2S3. The obtained Bi-Sb2S3 exhibited an increased photocurrent density, 2.8 mA cm−2 at 1.23 VRHE and a negative shift of onset potential, compared to bare Sb2S3. The enhancement in PEC performance of Bi-Sb2S3 could be attributed to the expanded light absorption range, increased electron carrier concentration and improved charge transfer ability.

Spinel-type ferrites decorated ZnO for enhanced photoelectrochemical water splitting

Among numerous semiconductor photoanodes, ZnO has been widely touted for its high electron mobility in the realm of Photoelectrochemical water splitting. However, some inevitable problems have limited its widening applications, such as narrow light photoresponse range and many surface defects. To this end, we first time demonstrate a novel strategy for CoFe2O4/ZnO and NiFe2O4/ZnO photoanodes by uncomplicated and inexpensive spin-coating and calcination stratagem. The optimal nanocomposite photoanodes showed excellent photocurrent density (2.3 folds higher than bare ZnO photoanode) and a negatively shifted onset potential of 75 mV. Moreover, due to the construction of Type-II heterojunction, the surface trap state of ZnO is reduced, the separation of photoproduced carriers is enhanced, the active sites are increased, and the interface reaction dynamics are accelerated.

Rational construction of S-doped FeOOH onto Fe2O3 nanorods for enhanced water oxidation

Hematite-based photoanode (α-Fe2O3) is considered the promising candidate for photoelectrochemical (PEC) water splitting due to its relatively small optical bandgap. However, severe charge recombination in the bulk and poor surface water oxidation kinetics have limited the PEC performance of Fe2O3 photoelectrodes, which is far below the theoretical value. Herein, a new catalyst, S-doped FeOOH (S-FeOOH), has been immobilized onto the surface of the Fe2O3 nanorod (NR) array by a facile chemical bath deposition incorporated thermal sulfuration process. The grown S-FeOOH layer acts not only as an efficient catalyst layer to accelerate the water oxidation on the surface of photoelectrode but also constructs a heterojunction with the light absorption layer to facilitate the interface charge carrier separation and transfer. As expected, the modified S-FeOOH@Fe2O3 photoanode achieves a remarkable increase in PEC performance of 2.30 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (VRHE) andan apparent negative shifted onset potential of 250 mV in comparison with pristine Fe2O3 (0.95 mA cm−2 at 1.23 VRHE). These results provide a simple and effective strategy to coupling oxygen evolution catalysts with photoanodes for practically high-performance PEC applications.

A Semiconductor-Mediator-Catalyst Artificial Photosynthetic System for Photoelectrochemical Water Oxidation.

In fabricating an artificial photosynthesis (AP) electrode for water oxidation, we have devised a semiconductor-mediator-catalyst structure that mimics photosystem II (PSII). It is based on a surface layer of vertically grown nanorods of Fe2 O3 on fluorine doped tin oxide (FTO) electrodes with a carbazole mediator base and a Ru(II) carbene complex on a nanolayer of TiO2 as a water oxidation co-catalyst. The resulting hybrid assembly, FTO|Fe2 O3 |-carbazole|TiO2 |-Ru(carbene), demonstrates an enhanced photoelectrochemical (PEC) water oxidation performance compared to an electrode without the added carbaozle base with an increase in photocurrent density of 2.2-fold at 0.95 V vs. NHE and a negatively shifted onset potential of 500 mV. The enhanced PEC performance is attributable to carbazole mediator accelerated interfacial hole transfer from Fe2 O3 to the Ru(II) carbene co-catalyst, with an improved effective surface area for the water oxidation reaction and reduced charge transfer resistance.

Proposal of a Facile Method to Fabricate a Multi-Dope Multiwall Carbon Nanotube as a Metal-Free Electrocatalyst for the Oxygen Reduction Reaction

In this study, a one-pot, low-temperature synthesis method is considered for the fabrication of heteroatom dope multiwall carbon nanotubes (MWCNT). Doped MWCNT is utilized as an effective electrocatalyst for oxygen reduction reaction (ORR). Single, double, and triple doping of boron, nitrogen and sulfur elements are utilized as the dopants. A reflux system with temperature of 180 °C is implemented in the doping procedure. Actually, unlike the previous studies in which doping on the carbon structures was performed using a furnace at temperatures above 700 °C, in this green and sustainable method, the triple doping on MWCNT is conducted at atmospheric pressure and low temperature. The morphology and structure of the fabricated catalysts were evaluated by Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Raman spectroscopy. According to the results, the nanoparticles were encapsulated in the carbon nanotubes. Aggregated clusters of the sulfur in the case of S-MWCNT are considerable. Cyclic voltammetry (CV), rotating disk electrode, linear sweep voltammetry (LSV), and chronoamperometry electrochemical tests are employed for assessing the oxygen reduction activity of the catalysts. The results illustrate that by using this doping method, the onset potential shifts to positive values towards the oxidized MWCNT. It can be deduced that by doping the N, B, and S atoms on MWCNTs, the defects in the CNT structure, which serve as active sites for ORR application, increase. The N/S/B-doped graphitic layers have a more rapid electron transfer rate at the electrode/electrolyte interface. Thus, this can improve the electrochemistry performance and electron transfer of the MWCNTs. The best performance and electrochemical activity belonged to the NB-MWCNT catalyst (−0.122 V vs. Ag/AgCl). Also, based on the results gained from the Koutecky–Levich (KL) plot, it can be said that the ORR takes place through the 4 e− pathway.

Oxygen reduction activity of Fe/Co/Ni doped MnOx @ graphene nanohybrid: A comparative study

• Fe, Co, and Ni doped MnO x was grown on NG. • Doped catalysts show better ORR activity than the undoped one. • Doping can tune the Mn valence. • Enhanced activity for doped MnO x owing to increase in Mn valence on doping. We report the electrochemical activity of transition metal ion (Fe, Co and Ni) doped MnO x @ N -graphene (MnO x @NG) hybrid catalysts towards oxygen reduction reaction (ORR). The doped catalysts displayed significantly enhanced electrochemical performance than the undoped one. The Fe doped MnO x @NG exhibited highest positive shift in onset potential (0.93 V vs. RHE), highest electron transfer number (n) (3.87) and lowest peroxide yield (6.35 %) in 0.1 M KOH solution. The Co doped catalyst showed highest current density, which is comparable to that of benchmark 20 wt% Pt/C. The XRD analysis showed that the catalyst samples are poorly crystalline and the doping of either Fe or Co or Ni cation induces formation of Mn 2 O 3 , whereas the undoped catalyst consists of both Mn 2 O 3 and MnOOH. The STEM (scanning transmission electron microscope) micrographs revealed that in all the samples the MnO x nanostructures are well dispersed on NG and the elemental mapping of the doped catalysts showed uniform distribution of dopants. The X-ray photoelectron spectroscopy (XPS) studies revealed that doping of either cation results an increase in the average Mn valency of the host MnO x . The change in crystal structure and corresponding ORR activity has also been investigated with increase in dopant amount for Fe doped samples.

Ultrafine platinum nanoparticles supported on N,S-codoped porous carbon nanofibers as efficient multifunctional materials for noticeable oxygen reduction reaction and water splitting performance.

The design of highly active, stable and durable platinum-based electrocatalysts towards the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and hydrogen adsorption has a high and urgent demand in fuel cells, water splitting and hydrogen storage. Herein, ultrafine platinum nanoparticles (Pt NPs) supported on N,S-codoped porous carbon nanofibers (Pt–N,S-pCNFs) hybrids were prepared through the electrospinning method coupled with hydrothermal and carbonation processes. The ultrafine Pt NPs are sufficiently dispersed and loaded on pCNFs and codoped with N and S, which can improve oxygen adsorption, afford more active sites, and greatly enhance electron mobility. The Pt–N,S-pCNFs hybrid achieves excellent activity and stability for ORR with ∼70 mV positive shift of onset potential compared to the commercial Pt/C-20 wt% electrocatalyst. The long-term catalytic durability with 89.5% current retention after a 10 000 s test indicates its remarkable ORR behavior. Pt–N,S-pCNFs also exhibits excellent HER and OER performance, and can be used as an efficient catalyst for water splitting. In addition, Pt–N,S-pCNFs exhibits an excellent hydrogen storage capacity of 0.76 wt% at 20 °C and 10 MPa. This work provides novel design strategies for the development of multifunctional materials as high-performance ORR catalysts, water splitting electrocatalysts and hydrogen storage materials.

Decoration of graphene oxide as a cocatalyst on Bi doped g-C3N4 photoanode for efficient solar water splitting

• Improvement of photoelectrocatalytic properties of Bi@g-C 3 N 4 by loading GO. • Enhancement in applied bias photon to current efficiency by cascade charge transfer. • The smallest semicircle in Nyquist plots for Bi@g-C 3 N 4 /GO. To enhance the solar photoelectrocatalytic water splitting, an effective photoanode was designed by electrophoretic depositing of graphene oxide (GO) on FTO/c-TiO 2 /Bi@g-C 3 N 4 . The photoelectrocatalytic performance of g-C 3 N 4 was improved by Bi doping and GO loading as a cocatalyst on the surface of photoanode through the efficient charge cascade to increase an effective charge separation and reduce activation barriers for oxygen evolution reaction. The current–potential curve of Bi@g-C 3 N 4 /GO displayed about five and two times more photocurrent density (0.3 mA cm −2 at 1.23 V vs RHE) with respect to those of g-C 3 N 4 and Bi@g-C 3 N 4 , following with a 110 and 80 mV cathodically shifted onset potential, respectively. The conduction band edge was calculated using the flat band potential of the photocatalysts which was estimated by Butler-Gartner model. GO loading leads to yield the photo-voltage of 176 mV compared with 81 and 113 mV for g-C 3 N 4 and Bi@g-C 3 N 4 , respectively. The optimum of thickness of GO cocatalyst was 0.9 µm. If the thickness exceeds this optimum value, the recombination centers increase and active sites of photocatalytic layer are blocked. The charge separation and injection efficiency for Bi@g-C 3 N 4 /GO photoanode were determined by using H 2 O 2 as an effective hole scavenger. Among fabricated electrodes, Bi@g-C 3 N 4 /GO electrode represented the lowest charge transfer resistance. The results showed that much improvement in photoelectrocatalytic performance was achieved by GO loading on the surface of photoanode with respect to Bi doping in the structure of photocatalyst.