Selectively nucleotide‐derived RuP on N,P‐codoped carbon with engineered mesopores for energy‐efficient hydrogen production assisted by hydrazine oxidation

Integrating hydrogen evolution reaction (HER) with hydrazine oxidation reaction (HzOR) has an encouraging prospect for the energy‐saving hydrogen production, demanding the high‐performance bifunctional HER/HzOR electrocatalyst. Ruthenium phosphide/doped carbon composites have exhibited superior activity toward multiple electrocatalytic reactions. To explore the decent water‐soluble precursors containing both N and P elements is highly attractive to facilely prepare metal phosphide/doped carbon composites. Herein, as one kind ecofriendly biomolecules, adenine nucleotide was first employed to selectively fabricate the highly pure RuP nanoparticles embedded into porous N,P‐codoped carbons (RuP/PNPC) with a straightforward “mix‐and‐pyrolyze” approach. The newly prepared RuP/PNPC only requires 4.0 and −83.0 mV at 10 mA/cm2 separately in alkaline HER and HzOR, outperforming most of reported electrocatalysts, together with the outstanding neutral bifunctional performance. Furthermore, the two‐electrode alkaline and neutral overall hydrazine splitting both exhibit significant power‐efficiency superiority to the corresponding overall water splitting with the voltage difference of larger than 2 V, which can be also easily driven by the fuel cells and solar cells with considerable H2 generation. Our report innovates the N‐ and P‐bearing adenine nucleotide to effortlessly synthesize the high‐quality RuP/doped carbon composite catalysts, highly potential as a universal platform for metal phosphide‐related functional materials.


INTRODUCTION
With the ever-escalating energy crunch and deteriorating global environment, exploiting clean renewable energy is evolving a stringent matter. 1,2The carbon-free hydrogen with the highest energy density is deemed as an extremely promising alternative to conventional fuels. 3,4ence, to develop environmentally friendly and highefficiency pathways of hydrogen generation is one core challenge for commercial popularization of hydrogen, therefore electrochemical overall water splitting (OWS) is regarded as the most appropriate technique, which includes two half reactions: the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER). 5Different from HER, OER involves intrinsically slow kinetics and high operating potential (1.23 V vs. RHE) arising from the multistep four-electron transfer process, which utterly brings an enormous obstacle to efficient water electrolysis, thus severely limits the large-scale application. 6Therefore, to substitute the OER by other anodic oxidation reactions with more favorable thermodynamics is significant for more affordable and efficient hydrogen generation. 7Among them, hydrazine oxidation reaction (HzOR, N 2 H 4 + 4OH − = N 2 + 4H 2 O + 4e − ) is engaging significant attention owing to the sufficiently low reaction potential of −0.33 V versus RHE and the safe and ecofriendly gaseous product of N 2 . 8,9Assembling HzOR with HER for the overall hydrazine splitting (OHzS) would drastically minimize the energy consumption during H 2 production, which thereby calls for the high-performance bifunctional electrocatalysts for HER and HzOR. 10 To date, transition metal-based electrocatalysts were largely studied for HER and HzOR, albeit with the economic cost, their activity especially for HER cannot come up to commercial Pt/C, [11][12][13][14][15] along with the intrinsically corrosion-prone defects under harsh conditions.7][18][19][20][21] In particular, ruthenium phosphides (RuP x ) display Pt-like activity for the wide-pH HER, probably because of the synergistic action of Ru metal and P on facilitating protons trapping and water dissociation during HER. 22,23Moreover, coupling RuP x with doped carbon can assure the benign electroconductivity of the composite catalysts, and further facilitate the dispersion of metal phase, more particularly, the binding between heterogeneous components can modulate the electronic properties of active sites for improved activity. 24,25Although some pioneering RuP x /doped carbons have been investigated, especially as HER electrocatalysts, 23,26 a few of the remaining issues need to be further studied.8][29] Oppositely, to seek the decent water-soluble precursors containing both N and P elements can hopefully address the above issues.Previously, acephate and 1,3,5-hexachlorotriphosphazene have been used as N and P precursors, but apparently they are toxic and expensive and not suitable for wide-scale applications. 30,31Second, RuP x -based HzOR electrocatalysts have been reported rarely to date, the understanding of RuP x mechanism during the HzOR behavior needs further research. 28,32Finally, HER and HzOR both involve the gas evolution process, moreover, the reactant N 2 H 4 has obviously large molecular size than that of H 2 O, thus the delicate porous structures play vital roles in enhancing their apparent activity from two aspects of active site exposure and mass transfer.In these cases, a facile synthetic strategy for RuP x /doped carbon with the favorable/select porosity still needs to be explored for bifunctional HER and HzOR.
Nucleotides are one type of common and ecofriendly biochemical molecules, containing the phosphate and N-bearing basic groups together with sugar moieties.Due to the structural diversity, nucleotides have been extensively employed to construct self-assembly systems and functional nanomaterials, 33,34 but it has never been used to prepare doped carbons or metal phosphides, as far as we know.Herein, we employ the ecofriendly adenine nucleotide to fabricate RuP nanoparticles/porous N,P-codoped carbon composites (RuP/PNPC) with high selectivity to RuP, therefore the larger mesopores created by silica can effectively expose the electrocatalytically active site, thus resulting in the superior bifunctional HER and HzOR performance in alkaline and neutral electrolytes.Especially, RuP/PNPC only requires 4.0 and −83.0 mV to drive 10 mA/cm for alkaline HER and HzOR, respectively, outperforming the most reported electrocatalysts.Additionally, the two-electrode alkaline and neutral OHzS both exhibit great energy-efficient superiority over the corresponding OWS with the difference of larger than 2 V.Meanwhile, the homemade N 2 H 4 /H 2 O 2 fuel cell (DHHPFC) and solar cell can readily power the alkaline OHzS with the decent H 2 generation of 1.42 and 1.28 mmol/h.

S C H E M E 1
The illustration of preparation route for RuP/PNPC.

Synthesis and characterization
RuP/PNPC was readily obtained by simple mixing and pyrolysis as illustrated in Scheme 1, simultaneously, RuP/N,P-codoped carbon (RuP/NPC) and porous N,Pcodoped carbon (PNPC) as the control samples were also synthesized by the similar routes with that of RuP/PNPC, but without silica and RuCl 3 , respectively.Noteworthily, the preparation conditions of RuP/PNPC were optimized in detail including the ratio of metal and adenosine 5'monophosphate disodium salt (AMP), the amount of silica template, and pyrolysis temperature (Figure S1).The x-ray powder diffraction (XRD) pattern was recorded to examine the metal status in different Ru-based catalysts.Remarkably, the pure RuP crystal phase can be selectively obtained at different conditions, indicating the superiority of the employed AMP (Figure S1).Typically, Figure 1A shows that both RuP/PNPC and RuP/NPC exhibit the similar metallic diffraction peaks located at 29.5, 32.2, 32.8, 44.6, and 46.6 • , separately corresponding to the (002), ( 011), ( 200), (112), and (211) planes of the RuP phase (JCPDS No. 65-1863). 28,35,36The pore size distribution analyses (Figure 1B and Table S1) demonstrate the obviously larger average pore size of 10.5 nm in RuP/PNPC due to the employment of 15-nm silica template with the pore volume of 1.02 cm 3 /g compared with those of RuP/NPC (4.2 nm and 0.25 cm 3 /g) and PNPC (5.7 nm and 1.66 cm 3 /g).Moreover, RuP/PNPC displays a Brunauer-Emmett-Teller (BET) surface area of 463 m 2 /g, but smaller than that of RuP/NPC (684 m 2 /g) and PNPC (1551 m 2 /g), maybe due to the formation of larger pores in RuP/PNPC.Meanwhile, the Raman spectrum was scanned to probe the textile structure of carbon.Figure 1C shows that the intensity ratio of D band to G band (I D /I G ) of RuP/PNPC is determined to be 0.91, less than that of RuP/NPC (0.98) and PNPC (0.96), indicating the higher degree of graphitization in RuP/PNPC.Furthermore, examination of the morphology measured by scanning electron microscopy (SEM) shows the interiorly porous structure in carbon matrix in Figure 1D.Transmission electron microscopy (TEM) bright-field image clearly illustrates the homogeneous RuP particles with the mean grain size of 6 nm isolatedly distributing on the carbon substrate of RuP/PNPC (Figure 1E,F).In the inset of Figure 1F, the lattice fringe with interplanar spacings of 0.237 nm is consistent with the (211) crystal planes of the RuP phase. 37TEM elemental mapping images show the coincident distribution of Ru and P (Figure 1G), also implying the formation of phosphide.As a contrast, the RuP/N,P-codoped carbon (RuP/NPC) and porous N,P-codoped carbon (PNPC) were obtained following the analogous approach (Figures S2  and S3).Without silica template, RuP/NPC sample also owns uniform and dispersed RuP nanoparticles with the average size of 11.0 nm, further suggesting the advantages of AMP precursor.Additionally, the metal-free PNPC exhibits the typical porously honeycomb-like structures with homogeneous N and P doping.The surface elemental status for catalysts was explored by x-ray photoelectron spectroscopy (XPS) (Figure 2, and Figures S4 and S5 and Table S2).The survey spectrum of RuP/PNPC in Figure 2A reveals the existence of C, P, N, O, and Ru.In the fitting spectra of P 2p (Figure 2B), two peaks located at 129.8 and 131.1 eV match up with the P 2p 3/2 and P 2p 1/2 of Ru-P bond, while the other two centered at 132.9 and 134.0 eV can be assigned to P-C and P-O bonds, respectively. 22,38For the high-resolution spectra of N 1s (Figure 2C), the peaks are primarily centered at 397.8, 399.8, 401.0, and 403.7 eV, consistent with pyridinic N, pyrrolic N, graphitic N, and oxidized N, respectively. 39he Ru 3d high-resolution spectrum in Figure 2D 2E) contain two groups of significant peaks, two ones at 461.7 and 484.1 eV are ascribed to 3p 3/2 and 3p 1/2 of metallic Ru bond, while the other two at 464.9 and 488.1 eV belong to 3p 3/2 and 3p 1/2 of Ru O bond. 16,40Figure 2F contrastively expounds the contents of componential elements among three samples.Excitingly, the most P and N heteroatoms in the form of P-C and graphitic N within AMP-derived carbon materials were favorable for electrocatalytical property.The Ru loading contents in RuP/PNPC and RuP/NPC were determined to be 28.97 and 14.99 wt% via inductively coupled plasma optical emission spectrometer (ICP-OES).This result verifies such a high loading, whereas Ru-based samples still maintain uniformly dispersed morphologies, showing the superiority of synthesis method with AMP.

Electrocatalytic HER to HzOR performance
The HER electrocatalytic performance of RuP/PNPC, RuP/NPC, PNPC, and Pt/C was evaluated in 1 M KOH electrolyte. 41Figure 3A presents a low overpotential of 4.0 mV at current density of 10 mA/cm 2 for RuP/PNPC, rather better than that of RuP/NPC (147.7 mV), PNPC (565.8 mV), and even Pt/C (23.5 mV).Moreover, it could be apparently detected that RuP/PNPC only needs 77.6 mV to attain a high current density of 100 mA/cm 2 , manifesting a much-splendid performance compared with RuP/NPC (385.4 mV) and Pt/C (194.9 mV), notably outperforming previously reported HER electrocatalysts including RuP x , 23,28,35,42 Ru particles, 16,[43][44][45] Ru single atoms, [46][47][48] Ru alloys, 49,50 and other Ru-based compounds (Table S3). 51,52Meanwhile, the Tafel slope of RuP/PNPC (52.4 mV/dec) manifests more beneficial catalytic kinetics than RuP/NPC (134.0 mV/dec), PNPC (563.1 mV/dec), and Pt/C (65.7 mV/dec) in Figure 3B.The ultrasmall chargetransfer resistance (R ct ) value of 1.8 Ω was obtained by electrochemical impedance spectroscopy (EIS) test (Figure 3C), indicating the fastest intrinsic electron transfer of RuP/PNPC in accord with Tafel slope trend.To evaluate the durability assessment, the amperometric I-t curve was carried out, and RuP/PNPC had extraordinary long-term stability with imperceptible current degradation after 10-h test (Figure 3C, inset).The above results convincingly verify the excellent electrocatalytic properties of the RuP/PNPC for the alkaline HER.To contribute an indepth understanding of HER activity, the electrochemical surface area (ECSA) can be analyzed with double-layer capacities (C dl ). Figure 3D and Figure S6 show the largest C dl value of 17.20 mF/cm 2 for RuP/PNPC, appreciably larger than that of PNPC (4.10 mF/cm 2 ) and RuP/NPC (0.61 mF/cm 2 ), suggesting that the larger mesopores on RuP/PNPC can efficiently expose the electrochemically active sites.Thus, the ECSA-normalized LSV curves were acquired for HER. Figure 3E displays a markedly higher current on RuP/PNPC, revealing its better intrinsic activity.Furthermore, the mass activities of different catalysts were evaluated based on the metal content (Figure 3F).RuP/PNPC possesses a much larger value of mass activity of 2.59 A/mg Ru at an overpotential of 100 mV than that of RuP/NPC (0.14 A/mg Ru ) and Pt/C (1.09 A/mg Ru ), implying more efficient atomic utilization in RuP/PNPC.
The HzOR activity of different samples was assessed in 1 M KOH containing N 2 H 4 . 41,53Initially, the effect of different hydrazine concentrations on HzOR performance was examined.Figure S7A shows an ignorable anodic current for electrolyte without N 2 H 4 .Nevertheless, the addition of 0.1-0.2M N 2 H 4 can result in the acutely lifted anodic current, which then minorly rises within the N 2 H 4 concentration scope of 0.3-0.5 M. Furthermore, the HzOR property with ultralow hydrazine concentrations was detected.Figure S7B reveals a superb linear dependence (R 2 = .998)for current density versus concentration within the range of 0-5 mM, obtaining a detection limit of 85 µM based upon the signal-tonoise ratio of 3, which illustrates capacious prospect for RuP/PNPC in the aspect of sensitive detection about N 2 H 4 . 32 activity at −83.0 mV to afford the current densities of 10 mA/cm 2 , greatly lower than that of RuP/NPC (62.5 mV), PNPC (632.1 mV), and Pt/C (167.7 mV).Remarkably, the potential gap between RuP/PNPC and compared catalysts becomes larger as the operation current density increases.Likely, RuP/PNPC only requires a less potential of −60.1 mV to drive 100 mA/cm in contrast to that of Pt/C (252.8 mV), also superior to that of most known HzOR catalysts including transition metal-and Ru-based particles, 10,11,16,54 single atoms, 55 phosphide, 28,32,56,57 nitride, 12,58,59 and selenide, 53,60 (Table S4).Furthermore, RuP/PNPC possesses the significantly better ECSA-normalized and mass activity for HzOR (Figure S8), also suggesting its incomparably intrinsic HzOR activity.Figure 3H displays that the Tafel slope of RuP/PNPC is 23.6 mV/dec, smaller than that of RuP/NPC (118.5 mV/dec), PNPC (293.0 mV/dec), and Pt/C (61.9 mV/dec).Furthermore, RuP/PNPC submits a lower R ct value (1.7 Ω) compared to RuP/NPC (44.0 Ω), PNPC (1696.0Ω), and Pt/C (7.2 Ω) as indicated in Figure 3I, verifying a prompt electron transfer for HzOR in alkaline media.The chronoamperometry measurement of the RuP/PNPC displays that the current density remains almost unchanged during consecutive 10-h operation (Figure 3I, inset), implying the splendid electrochemical durability in the alkaline conditions employed for HzOR test.
Impressively, RuP/PNPC also demonstrates a prominent HER activity in neutral 1 M PBS.The overpotentials of RuP/PNPC are 17.4 and 251.5 mV to achieve 10 and 100 mA/cm, respectively (Figure 4A), less than those of Pt/C (19.2 and 417.2 mV).The Tafel slope of RuP/PNPC was computed to 35.6 mV/dec, more favorable than that of RuP/NPC (168.4 mV/dec), PNPC (273.7 mV/dec), and Pt/C (35.8 mV/dec) (Figure 4B).In addition, RuP/PNPC has an apparently diminutive R ct value (16.5 Ω) compared with other samples and a highly stable chronoamperometry curve for 10 h, as described in Figure 4C.Furthermore, the neutral HzOR were measured in 1 M PBS with 0.1 M N 2 H 4 . 61 PNPC, and Pt/C catalyst are 155.8,157.2, and 72.8 mV/dec, respectively (Figure 4E).EIS analyses show that the R ct of RuP/PNPC (16.5 Ω) is superior among all catalysts, which implies the most contributive kinetics for HzOR (Figure 4F).As revealed in Figure 4F (inset), the potential is steady without drastic fluctuation of the RuP/PNPC during the whole chronopotentiometric measure process for 10 h.

Two-electrode OHzS performance
In order to certify the capacity in a two-electrode system for OHzS, 10 the RuP/PNPC was paired as both anodic and cathodic catalysts (Figure 5A).The loadings of electrocatalysts were installed to 0.5 mg/cm 2 on the carbon papers.As depicted in Figure 5B, the voltages of LSV curves are 0.011 and 0.145 V to attain 10 and 100 mA/cm 2 during OHzS process in 1 M KOH + 0.5 M N 2 H 4 solution, significantly smaller than those of Pt/C sample (0.233 and 0.495 V).Subsequently, the RuP/PNPC electrodes for OHzS and OWS were compared in K-OH with and without N 2 H 4 electrolyte (Figure 5C).The OWS electrolyzer requires high voltages of 1.739 and 2.393 V to attain 10 and 100 mA/cm 2 , respectively, greatly power-wasting compared to OHzS system.More importantly, the inset in Figure 5C presents that the voltage could be held stable after long-term measurement of 10 h.Additionally, the volumes of captured H 2 and N 2 through water drainage method in RuP/PNPC-based OHzS cell basically match the theoretically calculated quantities together with a perfectly stoichiometric H 2 :N 2 ratio of 2:1 (Figure 5D), suggesting almost 100% Faraday efficiency.A series of results ulteriorly show that the original morphology and structure were integrally preserved after long-term durability measurement (Figures S9 and S10), indicating the stabilized construction for RuP/PNPC.Besides, the neutral OHzS performance was also analyzed for RuP/PNPC electrodes.RuP/PNPC and Pt/C electrodes afford the voltages of 0.186 and 0.439 V to reach a current density of 10 mA/cm 2 , respectively (Figure 5E).It is also found from Figure 5F that the voltage of OWS cell (2.133 V) is much higher than that of OHzS at 10 mA/cm 2 , and 2.04 V higher than that for OHzS to achieve 30 mA/cm 2 .Moreover, the inset in Figure 5F demonstrates that RuP/PNPC almost maintains the original voltage during the 10-h process.The above consequences affirm that RuP/PNPC possesses robustly electrochemical and structural stability for OHzS.

OHzS performance powered by fuel cells and solar cells
Sparked by the outstanding HzOR behaviors of RuP/PNPC, the operating application expounded by measuring the direct liquid N 2 H 4 /H 2 O 2 fuel cell (DHHPFC) constructed by the RuP/PNPC catalyst as the anode in 4 M KOH with 1 M N 2 H 4 anolyte and commercial Pt/C catalyst as cathode in 0.5 M H 2 SO 4 with 5 M H 2 O 2 catholyte, respectively, and Pt/C was also individually paired as both anode and catholyte as comparison (Figure 6A). 62Figure 6B exhibits the open-circuit voltage (OCV) of 1.747 V for the RuP/PNPC-based DHHPFC, surpassing that of Pt/C (1.596 V).Likewise, a power density value of 136.0 mW/cm 2 is achieved for RuP/PNPC‖Pt/Cbased DHHPFC, higher than that of Pt/C‖Pt/C assembly (56.3 mW/cm 2 ), as shown in Figure 6C.Besides, the DHHPFC-powered OHzS system was further operated with the evolution of energetic bubbles on both anode cathode, and the amount of hydrogen yield was measured from the cathode with an eminent production rate of 1.42 mmol/h, in which RuP/PNPC demonstrates a satisfactory linear relationship with electrolysis duration, suggesting its foregrounds as high-efficiency electrocatalysts for large-scale applications in energy-saving H 2 production (Figure 6D).Meanwhile, the RuP/PNPC catalyst was also employed for solar cell-driven OHzS system using a commercial polycrystalline silicon solar cell with irradiation of the Xe light under ambient conditions (Figure 6E and Figure S11).Such a solar-driven H 2 production system also generates abundant bubbles under a working voltage of 1.44 V (Figure 6F), which attains the hydrogen yield with a rate of 1.28 mmol/h, verifying the feasibility of the RuP/PNPC catalyst in solar-driven holistic hydrazine splitting (Figure 6G).

CONCLUSION
In summary, the ecofriendly adenine nucleotide was first explored to selectively prepare the high-quality metal phosphide/doped carbon composite.Benefitting from the highly pure RuP, multiple doping in carbon and exposed active sites, the obtained RuP/PNPC possesses superior bifunctional HER and HzOR activity, and thus exhibits huge energy-saving advantage with OHzS in both alkaline and neutral conditions.The self-made DHHPFC and commercial solar cell can readily drive the alkaline OHzS with the considerable H 2 production, confirming the strong practicability of hydrogen production assisted by HzOR.This work provides a novel route by using low-cost ecofriendly biomolecules to synthesize functional nanomaterials for energy-related applications.

Preparation of RuP/PNPC
Typically, 1360 mg SiO 2 was ultrasonically added in 50 mL deionized water.After forming homogeneous solution, 39.77 mg RuCl 3 and 300 mg AMP were dissolved.The mixture was evenly dispersed by stirring for 12 h at room temperature and dried with rotary evaporation.Afterward, the solid was grinded to gray powder and then pyrolyzed at 900 • C for 1 h with a heating rate of 5 • C/min in a tube furnace at Ar atmosphere.Finally, the powder was etched with 6 M HF three times to remove SiO 2 and washed completely with deionized water by centrifugation.The collected sample RuP/porous N,P-codoped carbon was denoted as RuP/PNPC.

Preparation of RuP/NPC
To assess the effect of the porous structure, RuP/NPC was prepared from the same process as used for RuP/PNPC.RuP/N,P-codoped carbon was prepared using the same procedure without SiO 2 template, and the obtained sample was denoted as RuP/NPC.

Preparation of PNPC
As a control, the porous N,P-codoped carbon without Ru was also prepared using the same procedure as that of RuP/PNPC, and the obtained sample was denoted as PNPC.

A C K N O W L E D G M E N T S
This work was financially supported by the Development Project of Youth Innovation Team in Shandong Colleges and Universities (2019KJC031), Natural Science Foundation of Shandong Province (ZR2019MB064 and ZR2021MB122), and Doctoral Program of Liaocheng University (318051608).

C O N F L I C T O F I N T E R E S T S TAT E M E N T
The authors declare no conflict of interest.

R E F E R E N C E S
is deconvoluted into eight peaks, the peaks at 279.8 and 283.8 eV belong to 3d 5/2 and 3d 3/2 of metallic Ru bond, meanwhile the peaks at 280.4 and 284.4 eV correspond to 3d 5/2 and 3d 3/2 of Ru-O bond, and the peaks at 284.2, 285.3, 286.1, F I G U R E 1 (A) The XRD patterns of RuP/PNPC and RuP/NPC.(B) The pore size distribution curves (inset shows N 2 adsorption-desorption isotherms) and (C) Raman spectra of RuP/PNPC, RuP/NPC, and PNPC.(D) SEM image, (E and F) TEM images at different magnifications with the corresponding RuP size distribution and (G) TEM elemental mapping images of C, N, O, P, and Ru of RuP/PNPC.and 286.8 eV can be ascribed to C C, C N, C OH/C P, and C O moieties, respectively.The Ru 3p high-resolution spectra (Figure

F
I G U R E 2 (A) XPS survey scan and high-resolution XPS spectra of (B) P 2p, (C) N 1s, (D) Ru 3d, and (E) Ru 3p spectra of RuP/PNPC.(F) The comparison of elemental contents in RuP/PNPC, RuP/NPC, and PNPC samples.

F
I G U R E 3 (A) HER LSV curves of RuP/PNPC, RuP/NPC, PNPC, and Pt/C in 1 M KOH.(B) Tafel slopes of HER LSVs.(C) EIS and chronoamperometric test of RuP/PNPC in 1 M KOH.(D) The calculated C dl values based on the corresponding difference in the current density at 1.005 V plotted against scan rates.(E) The ECSA-normalized LSVs of HER.(F) The mass activity of different samples for HER.(G) LSV curves of HzOR in 1 M KOH with 0.5 M N 2 H 4 .(H) Tafel slopes of HzOR LSVs.(I) EIS and chronoamperometric test of RuP/PNPC in 1 M KOH with 0.5 M N 2 H 4 .
Figure 3G compares the HzOR LSV curves of different catalysts in 1 M KOH containing 0.5 M N 2 H 4 .Remarkably, RuP/PNPC shows splendid HzOR F I G U R E 4 (A) HER LSV curves of RuP/PNPC, RuP/NPC, PNPC, and Pt/C in 1 M PBS.(B) Tafel slopes.(C) EIS and chronoamperometric test of RuP/PNPC in 1 M PBS.(D) HzOR LSV curves in 1 M PBS with 0.1 M N 2 H 4 .(E) Tafel slopes.(F) EIS and chronoamperometric test of RuP/PNPC in 1 M PBS with 0.1 M N 2 H 4 .
Figure 4D shows a potential of 156.5 mV for RuP/PNPC to achieve 10 mA/cm, obviously superior than that of RuP/NPC (856.2 mV), PNPC (908.0 mV), and Pt/C (311.3 mV).The corresponding Tafel slope of RuP/PNPC is 57.2 mV/dec, whereas the Tafel slopes of RuP/NPC, F I G U R E 5 (A) Schematic illustration of the two-electrode OHzS electrolyzer.(B) Two-electrode LSV curves of alkaline OHzS with RuP/PNPC and Pt/C as bifunctional electrodes.(C) LSV curves of alkaline OHzS and OWS with RuP/PNPC (inset: the chronoamperometric test for alkaline OHzS).(D) The amount of H 2 and N 2 theoretically calculated and experimentally measured with RuP/PNPC in alkaline OHzS.(E) Two-electrode LSV curves of neutral OHzS with RuP/PNPC and Pt/C as bifunctional electrodes.(F) LSV curves of neutral OHzS and OWS with bifunctional RuP/PNPC (inset: the chronoamperometric test for neutral OHzS).

F I G U R E 6
(A) Schematic illustration and working principle of DHHPFC-powered OHzS system.(B) Open-circuit voltage of the RuP/PNPC||Pt/C and Pt/C||Pt/C DHHPFCs.(C) Discharge polarization curve and power density plot of the DHHPFCs.(D) The H 2 production from the DHHPFC-powered OHzS and OWS system.(E) Schematic illustration of the assembled solar cell-powered OHzS system.(F) Digital photograph of the evolution of gas bubbles on bifunctional RuP/PNPC electrodes.(G) The H 2 production from the solar cell-powered OHzS and OWS system.