Layer-selective hydrogenation and proton transport in twisted bilayer graphene

Domain: physics
Published: 2026-04-04
Editorial outcome: major_revision

Abstract
Recent work investigated graphene’s hydrogenation with independent control of the electric field, E, and charge density, n, in the crystal and showed that the process is controlled by n. Here, we demonstrate layer-selective conductor–insulator transitions in twisted bilayer graphene, driven by hydrogenation at fixed n under strong E. This process is accompanied by proton transport through the bilayer, enabling several parallel and configurable logic gates in the devices. Selectivity arises because the large twist angle decouples the two layers’ electronic systems, enabling independent control of their charge densities. Polarisation by the field then induces a charge imbalance at fixed total n, triggering hydrogenation when one of the layers’ charge densities reaches the threshold for monolayer hydrogenation. Our results introduce a new type of electrode-electrolyte interface in which electrochemical processes are controlled with two decoupled 2D electron gases, opening new design opportunities for energy and information processing devices.

Introduction
In a classical electrode-electrolyte interface, the applied potential couples the charge density, n, and the electric field perpendicular to the electrode, E, via parameters, such as solvent polarisability or Debye length1,2. In contrast, electrostatically gating a 2D crystal on both of its surfaces—a technique known as double gating—enables independent control of E and n in the crystal3-8. This decoupling expands the parameter space under experimental control, opening otherwise inaccessible pathways to drive electrochemical processes2. In recent work2, we applied this approach to a graphene electrochemical interface and demonstrated that it enables selective control of two otherwise coupled processes: proton transport through the crystal’s basal plane9-12 and proton chemisorption (hydrogenation)13-16. Proton transport was driven by E, and at high fields (~1 V nm-1) graphene became effectively transparent to protons. Conversely, hydrogenation was driven exclusively by n. This process led to a robust and reversible conductor-insulator transition in the crystal that, combined with the proton transport signal, enabled proton-based logic-and-memory operations in graphene2. Beyond electrochemical processes, double-gating has been routinely used to control diverse electronic phenomena in 2D heterostructures, such as ferroelectric switching17,18 and bandgap quenching in 2D semiconductors3,19, or to optically map the chemical potential of electrons in 2D heterostructures8. These advances could enable new ways of controlling electrochemical processes via the field-tuneable electronic properties of 2D systems. In this work, we studied proton transport and hydrogenation in non-aligned bilayer graphene. Although the two graphene layers are in direct contact, the large twist angle induces a momentum mismatch between electrons in each layer, which decouples their wavefunctions20-22. This constitutes a new type of electrode-electrolyte interface and remains unexplored.

Results
The devices for this work were fabricated by suspending mechanically exfoliated, non-aligned bilayer graphene over a 10 μm hole etched in a silicon nitride (SiNx) substrate (Fig. 1 and Supplementary Fig. 1&2). The suspended membranes were coated on both sides with a non-aqueous, proton-conducting electrolyte—bis(trifluoromethane)sulfonimide (HTFSI) in polyethylene glycol—with a wide electrochemical stability window (>4 V). The devices were contacted with two palladium hydride (PdHx) electrodes and connected to the electrical circuit shown in Fig. 1b (‘Device fabrication’ in Methods). Two gate voltages, Vt and Vb, were applied between the bilayer and the respective PdHx electrodes, enabling independent control of the potential at each graphene–electrolyte interface (Supplementary Fig. 3)2,3. We studied two electrochemical processes. The first was the electrochemical hydrogenation of twisted bilayer graphene. Graphene’s hydrogenation is characterised by a reversible conductor-insulator transition in the crystal, accompanied by a D band in its Raman spectra2,13,23. To monitor this process, we measured the in-plane electronic conductivity of each layer independently as a function of Vt and Vb, by applying in-plane source-drain voltages to each layer, Vtds and Vbds. Alternatively, we measured the electron tunnelling current and voltage between the two layers. The second process was out-of-plane proton transport2,9,10, which is characterised by the current in the electrolyte gates. We studied these processes with independent control of the electric field and charge density in the double-gated crystal. As established in multiple works3-8, the electric field is determined by the difference in the gate voltages, E ∝ Vt - Vb, and the charge density, n, by their sum, Vt + Vb (‘Estimation of E and n’ in Methods).

We started by investigating these processes under much higher E than in our previous work, while fixing the charge density at n ≈ 5×1013 cm-2, which is below the threshold required to hydrogenate graphene found in refs.2,13 (1×1014 cm-2). Starting with proton transport, the bottom panel of Fig. 1c shows that the electric field drove protons through the bilayer, yielding currents about 100 times lower than in monolayer graphene2 for the same E. This arises for two reasons. First, AB-stacked bilayers are impermeable to protons2,9, so proton transport can be expected to take place through AA-stacked regions, which occupy only ≈30% of the crystal’s area24. Second, AA-stacked regions in the bilayer pose a larger barrier to incoming protons than monolayer graphene (Supplementary Fig. 4). Unexpectedly, for a sufficiently high electric field, the layer facing incoming protons was hydrogenated, even though n remained constant and below the threshold required to enable this process. The hydrogenation of this layer was evidenced by a conductor-insulator transition in its electronic response, accompanied by a prominent D band in the sample’s Raman spectrum (Fig. 1c&e). Notably, only this layer was hydrogenated, and the resulting single-layer insulating state was stable for over 24 hours under constant gate voltages, demonstrating robust state retention (Fig. 1f). Reducing E below ~0.5 V nm⁻¹ (at constant n), recovered the layer’s conductivity, yielding a hysteretic electronic response and the disappearance of the Raman D band (Supplementary Fig. 5). The selective hydrogenation process was highly reproducible, displaying ON/OFF ratios of >104 with cycle-to-cycle variation of less than 6% for over 1000 cycles without degradation (Supplementary Fig. 6). The hydrogenation process was symmetric with respect to the direction of the electric field. Reversing the polarity of the field at fixed n reversed the direction of proton flow, and now the opposite layer was hydrogenated (Fig. 1d). These results demonstrate that a strong E in twisted bilayer graphene can enable layer-selective hydrogenation even at n previously considered too low to sustain this process.

We then characterised this process for various fixed n. To that end, we measured electron tunnelling between the two layers, which provides a four-probe, single-signal characterisation of the devices’ electronic properties and, since hydrogenation of either layer suppresses tunnelling, it characterises the insulating transition (Fig. 2a). During the measurements, we fixed n and swept E in a single polarity (E>0) to minimise exposure of the devices to extreme fields and ensure stability. Figure 2b shows that for n < 5×1013 cm2 (Vt + Vb < 1 V), no insulating transition was observed within the range of E applied; whereas for n = 5×1013 cm-2, the system reached the insulating state at high E, as discussed above. However, as n increased, we found that the field required to reach the insulating state decreased, and for large n>2×1014 cm-2 (Vt + Vb > 4 V), it was reached even at E=0. These observations show that lower charge density requires a stronger electric field to induce hydrogenation in this system.

To understand these findings, we measured the full E-n map of the electronic response (Fig. 2d). This revealed that the device displayed two neutrality curves, rather than the single neutrality line in monolayer graphene2 and AB-stacked bilayer graphene (Supplementary Fig. 7, ‘AB stacked bilayers’ in Methods). The splitting of the neutrality line has been reported previously and shown to arise from the polarisation of the crystal under the applied E20. However, in double-ionic-gated devices E is much stronger than in devices with solid-state dielectrics, which strongly polarise the bilayer, and now yield a clear X-shaped splitting, consistent with the functional form predicted theoretically20 (Fig. 2d inset, Supplementary Fig. 9 ‘Splitting of neutrality line’ in Methods). To the right of each curve, the corresponding layer is electron-doped; and to the left, hole-doped, creating distinct regions in the map corresponding to pp, np, and nn layer-doping configurations. This reveals that hydrogenation takes place when at least one of the layers is electron doped. Time-resolved layer-selective electronic measurements under fixed gate voltages (Fig. 2c), showed that for regions in which only the top layer is strongly electron doped (box 1, Fig. 2c&d), the top layer was hydrogenated; and in regions in which both layers were strongly n-doped (box 2, Fig. 2c&d), both layers were hydrogenated. The map also reveals that the boundary of the hydrogenated region in the map runs alongside the neutrality curves of the top and bottom layers (marked with arrows in Fig. 2d).

These findings are readily understood from our analytical model of the charge density in the bilayer (Supplementary Fig. 8). The model shows that the boundaries correspond exactly to voltage combinations for which n in one of the layers reaches 1014 cm-2. Hence, in the region containing box 1, only one layer has n >1014 cm-2, whereas in the region containing box 2, both layers do. This reveals that selective hydrogenation arises from electric-field-induced polarisation of the crystal, which drives n in one layer above 1014 cm-2 and <1014 cm-2 in the other. The highly charged layer then undergoes hydrogenation via the same mechanism demonstrated in our earlier work on monolayer graphene, where hydrogenation took place at this charge density2. These results thus explain our earlier observation that lower total carrier density requires higher electric fields—namely, under less total charge, stronger polarisation is necessary to accumulate the threshold charge for hydrogenation in one of the layers.

To demonstrate robust control over these processes, we used them to construct logic gates (Fig. 3). The two gate voltages were defined as logic inputs IN1 and IN2, and the resulting electronic and proton currents were monitored using three measurement configurations. In Mode I, we measured the in-plane electronic current from each graphene layer independently (logic outputs OUT1 and OUT2). When the top layer was hydrogenated and became insulating, its electronic current dropped to the off state; when dehydrogenated, it returned to the on state. This yielded a NOT logic gate (“NOT A”) in the top layer with ON/OFF ratio of 104, and symmetrically, a “NOT B” gate in the bottom layer. In Mode II, we measured the in-plane current of one layer (top or bottom) as OUT1 and the interlayer tunnelling current between the two layers as OUT2. A “NOT” logic gate was achieved for OUT1, just like in Mode I. However, now the tunnelling current provided a different logic gate. When either the top or bottom layer was hydrogenated, the tunnelling current dropped to the off state, functioning as a NOR gate (OUT2), which is a universal logic gate. In Mode III, the two layers were electrically connected, and we measured the total electronic current (OUT1). Only when both layers were hydrogenated did the current drop to a low state, thus implementing a NAND gate—another universal logic gate. In all three modes, the out-of-plane proton current provided an additional parallel XOR logic gate with ON/OFF ratio of 102. These results therefore show that protons can be used to encode information in a configurable architecture that enables parallel logic operations within a single graphene device.

Our results introduce a new electrode-electrolyte interface with two decoupled 2D electron gases. We show that proton adsorption can be controlled by field-induced charge imbalances between individual layers, which is a new way to control chemical adsorption in surfaces and opens new pathways to drive electrochemical processes. We exploited the several degrees of freedom in this interface to enable configurable and parallel proton–electronic logic gates within a single device, an approach that could be extended to several of the 2D heterostructures being intensely researched in electron transport studies. Beyond this, the new interface demonstrated here could enable novel control protocols for other processes governed by electronic charge density, such as ion intercalation or redox processes, opening new design opportunities for energy technologies and ion-based information processing in van der Waals heterostructures.

Methods
Device fabrication. Apertures 10 µm in diameter were etched into silicon nitride substrates (comprising a 500 nm SiNₓ layer on both sides of a silicon wafer) using a combination of photolithography, wet etching, and reactive ion etching, as reported previously9. Two pairs of electrodes (Au/Cr) were patterned on the substrate using photolithography and electron beam evaporation. Two mechanically exfoliated graphene flakes, each with a rectangular shape (tens of micrometres in length and approximately 10 µm in width), were stacked on opposite sides of an hBN layer with a thickness of 10-20 nm. The hBN layer contained a circular hole, aligned in size and position with the hole in the underlying SiN substrate (Supplementary Fig. 1). The graphene flakes were assembled in a cross configuration, centred on the circular hole, such that each flake was individually contacted by a pair of Au electrodes. In this design, the graphene bilayer is electrostatically gated from both sides, enabling double gating of the stacked structure. Crucially, the two graphene flakes are in physical contact with each other only in the central, gated region—defined by the aperture in the hBN and SiNₓ layers—where both flakes are exposed to the electrolyte. This configuration ensures that any changes in conductivity due to hydrogenation are detectable. Specifically, if one graphene layer becomes hydrogenated and thus insulating, electron transport across that layer is suppressed because the two flakes are not electrically connected outside the gated area. In contrast, without the hBN spacer, the flakes would be in contact over a larger area, allowing current to bypass the hydrogenated region through ungated or unexposed parts of the other flake, masking the effects of hydrogenation.

An SU-8 photo-curable epoxy washer with a 15 μm-diameter hole was transferred over the assembly and on the source and drain electrodes12 with the hole in the washer aligned with the aperture in the silicon-nitride substrate (Supplementary Fig. 1) to ensure that the electrodes are electrically insulated from the electrolyte. The proton-conducting electrolyte used was 0.18 M bis(trifluoromethane)sulfonimide (HTFSI) dissolved in poly(ethylene glycol) (average molecular weight Mn of 600)13. Palladium hydride foils (~0.5 cm2) were used as gate electrodes. The device was placed inside a gas-tight chamber filled with argon for electrical measurements.

Transport measurements. A dual-channel Keithley 2614B sourcemeter was used to independently bias the top and bottom gates, while a second dual-channel Keithley 2636A sourcemeter was used to apply the drain–source bias and measure the in-plane electronic conductance of each graphene layer. We measured the electronic current of the devices in three different configurations (Modes I, II, and III). In Mode I, we recorded the conductance of each layer by applying drain-source voltages to each layer. In Mode II, we drove the interlayer tunnelling current, Itun, by applying a voltage VSds between the top and bottom layer and then recorded the resulting tunnelling voltage (Vtun) with a Keithley 2182A Nanovoltmeter. In Mode III, we measured the total in-plane electronic current by applying a single drain-source voltage to both layers. On the other hand, the proton current (I) was recorded by monitoring the gate currents on both the top and bottom channels, as previously reported2. All measurements were obtained using software that allowed controlling Vt - Vb and Vt + Vb as independent variables. To map the response of the samples, we swept Vt - Vb (for a fixed Vt + Vb) at a rate of 10 mV s-1 and stepped Vt + Vb with 10 mV intervals.

Note that previous works have established that in these devices the two gates are independent from each other2,3. We confirmed this here in the extended gate voltage range used in this work (Supplementary Fig. 3). This was done by adding a reference electrode to the top channel (a PdHx foil of the same size as the gate electrodes) and measuring its potential, Vref, with a Keithley 2182A Nanovoltmeter. These data showed that Vtref = Vt for all values of Vb within the experimental scatter of less than 5 mV. These data also demonstrate that the voltage drop takes place at the graphene electrode, with a negligible drop in the electrolyte, as expected for microelectrode devices25.

Raman spectroscopy. For Raman measurements, the samples were placed inside a gas-tight Linkam chamber (HFS600E-PB4), and spectra were collected using a 514 nm laser. Supplementary Fig. 2 shows that twisted bilayer graphene samples exhibit a blueshift in the 2D and G bands accompanied by a larger I2D/IG ratio. A ratio of I2D/IG <2 is associated with a twist angle within the range of 3°–15°26-28, whereas I2D/IG >2 indicates an angle within the range 15°–30°26-28. In both cases, the areal fraction of AA-stacked regions is estimated to be approximately constant at ≈30%24. Raman mapping across the entire sample area confirmed that the spectra were uniform across the sample, indicating a uniform twist angle throughout.

For in situ Raman measurements during the hydrogenation process, the spectra were acquired under constant gate voltages. The background signal from the electrolyte was subtracted for clarity, as reported previously2,13. Hydrogenation of a single graphene layer yields a strong D peak, similar to that observed for hydrogenated monolayer graphene previously2,13 (Supplementary Fig. 5). On the other hand, while the 2D peak was less intense than in pristine twisted bilayers, it remained defined2,13, as expected. Only if both layers were hydrogenated, the 2D peak was fully smeared. Crucially, the hydrogenation transition was fully reversible: the D peak disappeared completely from the Raman spectra following de-hydrogenation.

Scanning Transmission electron microscopy (STEM) imaging. For imaging, twisted bilayer graphene devices were fabricated on custom-made silicon nitride TEM grid coated with Ta (2 nm) & Au (20 nm) to enhance the adhesion of the stack to the grid and annealed at 400 ℃ under H2/Ar with a pressure of 1.2 bar for 13 hours. Atomic resolution high angle annular dark field (HAADF) STEM images were collected using an ThermoFisher Iliad Ultra STEM operated at 80 kV with an aberration-corrected probe, a 24 mrad probe convergence angle, and a HAADF inner angle of 80 mrad. STEM image analysis and filtering was performed using open-source python package Hyperspy version 2.3.0 [hyperspy v2.3.0 (Zenodo, 2025).].

Estimation of E and n. In our previous report2, we detailed the derivation29 of the well-established relations4,5,29-31 between the top (Vt) and bottom (Vb) gate voltages and E and µ. For twisted bilayer graphene, we have the same relation for the geometrical capacitance term: neC-1 = (Vt + Vb) - ΔNP, where ΔNP ≡ VtNP + VbNP, n = nt + nb is the total charge in the bilayer, nt (nb) is the charge density in the top (bottom) layer, and C is the area-normalised capacitance of the electrolyte (the value in our system is ≈ 20 µF cm-2 at a scan speed of 10 mV/s)2. To consider the quantum capacitance of graphene, we note that μ = ħvF(√π|nt|+√π|nb|) , with vF ≈ 1 x 106 m s-1 the Fermi velocity in graphene, and ħ the reduced Planck constant. This yields the relation to50:

(Vt + Vb) - ΔNP = neC-1 + ħ vF e-1(2πn)1/2. (1)

The formula for E is the same as in our previous work2:

E = Et - Eb = C (2ε) -1 (Vt - Vb), (2)

with ε = ε0 εr, ε0 the vacuum permittivity and εr ≈ 10 the solvent dielectric constant32,33. Introducing the numerical values of the parameters yields: (Vt + Vb) - ΔNP ≈ 0.8 x 10-14 V cm2 n + 1.64 x 10-7 V cm n1/2 and E ≈ 1.13 x109 V m-1 (Vt - Vb).

Splitting of the neutrality line. The graphene layers in bilayer graphene are modelled as two conducting thin plates which are electrostatically coupled by a capacitance Cm. This capacitance was determined in ref. 20 and found to be Cm ≈7.5 μF cm-2. The electrolyte potential profile in the electrolyte is modelled by a Gouy-Chapman-Stern model1 and results in an electrical double layer near the graphene surface. The gate potential almost exclusively drops over this Stern layer, which has a typical thickness2 of about 0.9 nm. The electrolyte is modelled by a capacitor with Ct ≈ 20 μF cm-2. Note that Ct/Cm ∼2.67, and thus we are in a very different regime from the hBN encapsulated twisted bilayer graphene investigated in ref. 20 where ChBN/Cm ∼0.11. Supplementary Fig. 8 shows a schematic of the analytical model.

From Gauss' law, we obtain:

Ct (V – VGt) - Cm (VGt – VGb) = – ent, (3a)

Cm (VGt – VGb) – Cb (VGb – Vb) = – enb , (3b)

where V, VGt, Vb, VGb are as defined in Supplementary Fig. 8b and the charge density on the graphene layers is determined by the Fermi energy EFi =  ħvF (π|ni|)1/2 in the layers: ni = -(eVGi)2(πħ2vF2)-1sgn(VGi) = -0.739x1014 VGi2sgn(VGi) where VGi is expressed in Volt and density in cm-2. A similar expression is obtained for nb. The neutrality line nt=0 is then obtained as:

Vb = – (γ+β)Vt – αβγ Vt2 sgn(Vt).

With β = Ct/Cb the asymmetry of the gates, γ = Ct/Cm the ratio of electrolyte capacity versus the bilayer graphene capacitance, and α = e3 Cm -1 (ħvF √π)-2 = Cm -1 x 11.8 μF cm-2 V-1. Similarly, we find for the other neutrality line nb = 0 that:

Vb = β(2αγ)-1(1+γ) sgn(Vt) {1– [1+4αγ(1+γ)-2 Vt sgn(Vt)] 1/2}

These equations are plotted directly into the map in Fig. 2d using Ct=Cb=20 μF cm-2 and Cm=7.5 μF cm-2, which results in γ=2.67, β=1, and α=1.57.

Analytical model. The voltage on the separate graphene layers (VGt, VGb) can be obtained from a self-consistent solution of the coupled non-linear equations Eq. (3a,b) which can be written as

γ (Vt – VGt) – (VGt – VGb) – αVGt2sgn(VGt) = 0, (4a)

(VGt – VGb) – γβ-1(VGb – Vb) – VGb2sgn(VGb) = 0. (4b)

From Eq. (4a), we solve for VGb and insert it into Eq. (4b), which results in the following 4th order algebraic equation ax4 + bx3 + cx2 + dx + e = 0 with x = VGt and the coefficients are given by:

a = α³ sgn(VGt), b = 2α²(γ + 1) sgn(VGt) sgn(VGb), c = -2α²γ Vt sgn(VGt) sgn(VGb) + α(γ + 1)2 sgn(VGt) + α(1 + γβ-1)sgn(VGb), d = -2αγ(γ + 1) Vt sgn(VGt) + γ(1 + γβ-1 + β-1)], e = αγ² Vt2 sgn(VGt) – γ(1 + γβ-1)Vt – γβ-1 Vb.

Inserting this solution into Eq. (4b) gives VGb.

Adding Eq. (3a) and Eq. (3b), we find for the total charge density on bilayer graphene under the assumption of Ct = Cb = C: n = nt + nb = Ce-1{Vt + Vb – (VGt + VGb)}.

DFT calculations. First-principles calculations were performed using VASP with plane-wave basis sets and the PAW method34-37. Van der Waals interactions were included using the DFT-D3 correction by Grimme35, and spin polarization was considered. Exchange–correlation energies were treated within the GGA-PBE functional36. A 500-eV energy cutoff and Monkhorst-Pack k-point mesh with a resolution of 2π×0.05/Å were used. Convergence thresholds were 10⁻⁶ eV (energy) and 0.01 eV/Å (forces). The simulation cell contained a 6×6 graphene supercell (72 atoms/layer) with periodic boundary conditions and a vacuum spacing of 20 Å in the z-direction to avoid image interactions. Different stacking configurations (AA′, AB, SP) were tested, and all atoms were fully relaxed. Transition states for hydrogenation and proton permeation were identified using Nudged Elastic Band (NEB) calculations.

Supplementary Fig. 4a shows the energy profile for a proton permeating through the central ring of twisted bilayer graphene (AA stacking). The barrier to pass through the first layer is 1.4 eV, consistent with previous works2,9. After entering the interlayer space, the energy profile shows a local minimum at the centre. This increases the barrier to pass the second layer to 1.7 eV, further suppressing proton transport. Since the AA-stacked regions occupy only ~30% of the total area, the reduced areal coverage and the higher barrier account for the lower proton flux compared to monolayer graphene observed experimentally.

Supplementary Fig. 4b shows hydrogen adsorption barriers for AA and AB stacked bilayers. In twisted bilayer graphene, hydrogenation barriers range from 0.05–0.20 eV. AB stacking shows particularly low barriers (<0.1 eV), ~50% less than in monolayer graphene (~0.2 eV). In contrast, AA stacking exhibits barriers similar to monolayer graphene. Adsorption wells of 0.9–1.1 eV were found, lower than for monolayer graphene, due to interlayer electronic effects that reduce the stability of the chemisorbed state and facilitate dehydrogenation.

Configurable parallel logic gate measurements. We implemented three logic modes using a single twisted bilayer graphene device by defining gate voltages Vt and Vb as logic inputs. Mode I uses in-plane currents from each graphene layer as outputs. Mode II uses both the in-plane electronic and interlayer tunnelling currents as output. Mode III uses total in-plane current. For all three modes, the proton current provides another parallel output. Logic operations were driven by square-wave gate voltages, with -1.2 V and +2.4 V representing logic input 0 and 1. All three modes used the same input signals, enabling straightforward configuration of the different logic gates within the device. For the these modes, the logic gates (NOT, NOR and NAND) using electron transport which based on the selective hydrogenation process show the ON/OFF ratios of 104 with cycle-to-cycle variation less than 5%, while the logic gates (XOR) using proton transport show show the ON/OFF ratios of 104 with cycle-to-cycle variation less than 10%.

To demonstrate the stability of the device during the selective hydrogenation and dehydrogenation process, a cyclability test were carried out based Mode I measurement configuration. For selective hydrogenation of the bottom layer while maintaining conductivity in the top layer, gate voltages of Vt and Vb were set to 0.9 V and 1.9 V, respectively. For dehydrogenation of the top layer, both Vt and Vb were set to be -1 V. Each hydrogenation–dehydrogenation cycle had a duration of 12.5 s.

AB-stacked bilayers. AB bilayers display fundamentally different proton transport and adsorption phenomena. First, these crystals are impermeable to protons, even under large fields. We demonstrated as shown in Supplementary Fig. 7e and in our previous works2,9. Second, because the two graphene layers in AB stacking are electronically coupled, it is not possible to induce layer-selective conductor–insulator transitions. When a sufficiently large potential is applied to one side, the upper surface of the bilayer can be hydrogenated, which is reflected by a conductance drop at the corresponding potential (Supplementary Fig. 7c). However, the bilayer remains overall conductive. Only when a large potential is subsequently applied to the opposite side, does the system undergo a full insulating transition (Supplementary Fig. 7d). These control measurements show that twist-induced electronic decoupling is essential for enabling both layer-selective hydrogenation and logic functionality.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This is a highly compelling study that introduces a novel electrode-electrolyte interface based on twisted bilayer graphene. It\nelegantly demonstrates how the decoupling of electronic systems in a van der Waals heterostructure can be harnessed for\nprecise electrochemical control and configurable logic operations. Several issues regarding device validation,\nperformance\nquantification, and operational stability will be essential for establishing its full impact and technological relevance.\nTherefore, a minor revision is necessary.\n1. The device configuration described in Extended Data Figure 1 shows that the two graphene layers are separated by a h-\nBN spacer and only make contact within a limited suspended area. This raises questions about whether the system truly\nfunctions as a coherent twisted bilayer graphene system or rather as two independent monolayers with partial contact.\nAdditional evidence, such as direct observation of Moiré patterns in tunneling spectroscopy, would help validate the twisted\nbilayer characterization and clarify how the electronic coupling in the contact region dominates the overall system behavior.\n2. The 24-hour state retention under constant gate voltages (Figure 1f) is impressive for memory applications, but the\npractical implementation requires demonstration of cyclical stability. While Raman data in Extended Data Fig. 5b suggests\nsome reversibility, complementary electronic transport data showing multiple hydrogenation-dehydrogenation cycles are\nlacking. Quantification of performance metrics such as ON/OFF ratio degradation over cycles would significantly strengthen\nthe application potential claims.\n3. The logic gate demonstration in Figure 3 is conceptually interesting, but lacks quantitative performance benchmarks.\nExplicit documentation of ON/OFF current ratios for each output under standardized conditions would enable proper\nevaluation of the logic operation quality. Additionally, characterization of switching speed and cycle-to-cycle variation would\nprovide crucial information for assessing practical applicability.\n4. While the manuscript highlights the advance beyond previous work on monolayer graphene, the introduction could more\nprecisely articulate the specific conceptual leap achieved by the decoupled bilayer architecture. The outlook section would\nbenefit from concrete examples of other 2D heterostructures where this approach could be applied, such as twisted\ntransition metal dichalcogenide systems for ion intercalation control.", "reviewer_2": "The authors report layer-selective protonation in twisted bilayer graphene using double electrolyte gating and further\ndemonstrate configurable logic operations. Independent control of the electric field and carrier density is claimed to modulate\nthe resistance of each layer. The results are intriguing, but several aspects of the mechanism and data interpretation require\nclarification, as follows:\n1. The authors analyze their data based on an electric field defined as E ∝ Vt - Vb. However, this definition is not physically\nreasonable in the double electrolyte gating. I suggest analyzing the results in terms of the individual gate voltages (Vt and\nVb), both their sign and magnitude, for the following reasons.\nThe electrolyte contains both cations and anions. Under positive bias, H+ ions migrate toward the graphene, while under\nnegative bias, TFSI- or O2- ions move toward the interface. TFSI- ions induce mainly electrostatic effects, whereas O2- ions\ncan lead to both electrostatic and electrochemical modifications of graphene. Thus, both types of negatively charged species\naffect the conductivity of graphene.\nWhen analyzing Fig. 2 by decomposing the data into Vt and Vb components, both top and bottom graphene layers show\nabrupt conductance decreases at approximately Vt (or Vb) = ~2 V. This appears to be a critical voltage corresponding to H+\nmigration into the respective layer. Therefore, the electric potential and field should be defined separately for each layer,\nrather than using a global Vt - Vb term, which is not sufficiently meaningful to describe layer-specific conductance changes.\n2. The assumption that carrier density is simply proportional to Vt + Vb is also not reasonable. This model implicitly assumes\nthat only H+ ions participate in gating. However, when Vt or Vb is negative, migration of TFSI- or O2- ions should also be\nconsidered. It would therefore be more reasonable to define and evaluate carrier density individually for each layer.\n3. The carrier density is estimated by simple equations, but such estimates are often inaccurate for electrolyte gating.\nIonic\ngating typically involves both electrostatic accumulation and electrochemical reactions, and electric-double layers are\nformed on the surface. This means that carrier density cannot be defined solely by applied voltage. I recommend directly\nmeasuring carrier density using Hall measurements or an equivalent experimental approach.\n4. The authors attribute independent modulation of the top and bottom layer resistances to electronic decoupling induced by\nthe large twist angle. However, the observed independence could simply result from the independent control of Vt and Vb for\neach layer, rather than from the twisted structure itself. It remains unclear whether the twist angle plays any essential role.\nI\nsuggest presenting twist-angle-dependent measurements to support this claim.\n5. TFSI-based ionic liquids are known to contain residual water, which allows migration of both H+ and O2- ions. Please\nrefer to previous reports showing H+ migration under positive bias and O2- migration under negative bias (Nature 2017, 546,\n124–128; ACS Nano 2022, 16, 6206–6214). H-TFSI systems are also hygroscopic, enabling H+ and O2- migration during\ngating. Therefore, it is highly possible that O2- ions migrate into graphene under negative Vt or Vb.\n6. The manuscript states that the top and bottom graphene layers are in contact within the aperture of the hBN layer. Please\nclarify the thickness of the hBN spacer and whether the two graphene layers are indeed in electrical contact. The data in Fig.\n2 suggest connection between layers, but the term “tunneling current” used to describe the measurement is confusing. It\nseems more appropriate to describe this simply as out-of-plane current between the two graphene sheets rather than\ntunneling through a barrier.", "reviewer_3": "The authors demonstrate hydrogenation and proton transport in twisted bilayer graphene. Based on AA stacked region in\ntwisted bilayer by employed hBN spacer with hole, the conductance variation of bilayer as a function of electric field of\nhydrogenation/de-hydrogeneration and top, bottom gate voltage (Vt and Vb). Since this manuscript introduces a layer\nselective proton transport characterization as well as its logic application of twisted bilayer graphene, this result will be a\ngood reference on electrolyte gating graphene research field. However, because the mechanically stacked bilayer graphene\nleads to various complex surface condition comparing with their previous paper about electrolyte gating study for\nmonolayer graphene (Ref. 2), more detail experimental results and explanations should be supplemented for publication.\nThe detailed comments are as follows.\n1. During mechanically stacking of graphene layers, undesired bubbles and wrinkles often arise and can influence\nconductance variability and proton transport in stacked bilayer graphene. Because authors analyze AA and AB stacking in\ntwisted bilayer graphene (TBG) including the associated area fractions and specific twist angles, it is important to distinguish\nintrinsic stacking effects from extrinsic disorder. To address this, please provide additional evidence and a deeper\nexplanation demonstrating that the contact/interfacial area of the twisted bilayer is clean and representative. In particular,\ndirect structural characterization (e.g., HRTEM) to map AA/AB domains without undesired bubbles and wrinkles would\nsubstantially strengthen the manuscript.\n2. Authors propose that AA-stacked bilayer graphene hydrogenates at a lower charge-density threshold than monolayer\ngraphene (Ref. 2) and attribute this to electric-field differences. For clarity, please articulate the discussion of which physical\nfactors most plausibly account for the reduced threshold. Framing the observation within these mechanisms would\nstrengthen the manuscript.\n3. For finding neutrality line, authors employed calculation with capacitance values extracted from references. Furthermore,\nsince the extended data Fig. 6 exhibits CNP for natural (Bernal) stacked bilayer, we can easily observe the single CNP for\nBernal (AB) stacked bilayer graphene. However, if there are layer selected conductance variation for top and bottom\ngraphene, we could observe charge neutrality position (CNP) of transport curve for top and bottom monolayer graphene as a\nfunction of Vt or Vb, respectively. Furthermore, we will observe more mixed CNP behavior dependent on twisted bilayer\ngraphene area. I can also see CNP shapes as a function of E for conducting condition of top and bottom layer in Fig. 1 c and\nd. If authors exhibit externally experimental CNP behavior as well as discussion about it, their manuscript will be more\nstrengthened, too.\n4. There should be mentions for scale bar sizes in extended data Fig.2 b, c and Fig. 6 a.", "reviewer_4": "The manuscript presents an elegant and conceptually innovative study of electrochemical hydrogenation and proton\ntransport in twisted bilayer graphene (TBG) under dual ionic gating. Building on the authors’ recent paper in Nature\ndemonstrating decoupled control of proton transport and hydrogenation in monolayer graphene, this work extends the\nparadigm to twisted bilayers, exploiting twist-induced electronic decoupling to achieve layer-selective hydrogenation and\nlogic operations within a single device. This represents a significant advance: by leveraging the independent carrier\ndensities emerging from the two-layer electronic systems of large-angle TBG, the authors introduce a new type of electrode–\nelectrolyte interface in which electrochemical processes can be spatially and electronically partitioned at room temperature.\nThe demonstration of configurable NOT, NOR, NAND, and XOR logic elements—arising from a single material platform and\ncontrolled solely via gate voltages—is very nice, and opens promising avenues for ion–electron hybrid information\nprocessing.\nThe experimental methodology is sound, and the characterization (conductance mapping, tunneling measurements, Raman\nspectroscopy, and DFT calculations) provides a largely coherent picture of the underlying processes. The work is also\nclearly novel relative to the group’s earlier monolayer study: the ability to target hydrogenation to an individual graphene\nlayer at fixed overall charge density, and to use this selectivity as a functional device degree of freedom, is new, nontrivial,\nand likely to be of broad interest to the community.\nThat said, two aspects of the study would benefit from further clarification and tempering of claims.\n1. Lack of systematic controls on untwisted (AB-stacked) bilayer graphene.\nThe manuscript includes only a minimal control measurement on AB-stacked bilayers—\nnamely, a conductance map\nshowing a single neutrality line. While this does verify the expected absence of layer decoupling, it does not test whether\nhydrogenation, proton transport, or logic functionality differ qualitatively from the twisted case. Because the main claims rely on the\nemergence of layer-selective behavior due to twist-induced electronic isolation, a more complete comparison with\nuntwisted bilayers would significantly strengthen the conclusions. Even basic measurements—such as whether AB bilayers\nundergo single-layer or simultaneous dual-layer hydrogenation under equivalent fields, or whether proton transport is\nobservable at all—would help establish that the observed phenomena are uniquely rooted in twist-angle physics rather than\nmore general features of bilayer graphene under high electric fields.\n2. Interpretation of the AA-stacked regions as the exclusive proton-transport pathway.\nThe manuscript repeatedly attributes proton permeation primarily to AA regions of the Moiré superlattice. Although this\ninterpretation is physically plausible and supported by DFT barrier calculations, it remains hypothetical within the context of\nthe experimental data presented. The proton-current measurements are spatially unresolved, and no experiment directly\nevidences transport localization to AA regions or correlates permeation with twist-angle-dependent AA area fraction. I\nrecommend that the authors moderate the certainty of these claims and clarify that the AA contribution, while consistent with\ntheoretical expectations, is not experimentally demonstrated. Future work—such as twist-angle dependence studies,\nspatially patterned gating, or correlated imaging—could substantiate this point.\nIn summary, this is a strong manuscript that presents noteworthy advances in electrochemical control of two-dimensional\nheterostructures. With a modest softening of the AA-region interpretation and consideration of additional bilayer-control\nmeasurements, the paper will provide a clearer and more rigorously supported account of an important new\nelectrochemical phenomenon in twisted bilayer graphene. I find the work to be of high quality and recommend publication after these points are addressed."}, "author_response": "Response to comment from Reviewer #1\nThis is a highly compelling study that introduces a novel electrode-electrolyte interface based\non twisted bilayer graphene. It elegantly demonstrates how the decoupling of electronic\nsystems in a van der Waals heterostructure can be harnessed for precise electrochemical\ncontrol and configurable logic operations. Several issues regarding device validation,\nperformance quantification, and operational stability will be essential for establishing its full\nimpact and technological relevance. Therefore, a minor revision is necessary.\nWe are very grateful to the Reviewer for this encouraging assessment of our work. We have\nperformed additional measurements, device characterisation and included new discussion to\naddress the points raised.\n1. The device configuration described in Supplementary Figure 1 shows that the two graphene\nlayers are separated by a h-BN spacer and only make contact within a limited suspended area.\nThis raises questions about whether the system truly functions as a coherent twisted bilayer\ngraphene system or rather as two independent monolayers with partial contact. Additional\nevidence, such as direct observation of Moiré patterns in tunneling spectroscopy, would help\nvalidate the twisted bilayer characterization and clarify how the electronic coupling in the\ncontact region dominates the overall system behavior.\nThe two graphene layers make direct contact across the entire suspended region, whose area\nis almost identical to their full geometric overlap (Supplementary Fig. 1c). Three independent\nmeasurements confirm that the system operates as a coherent twisted bilayer rather than two\ndecoupled monolayers. First, the transport maps show a non-trivial splitting of the neutrality\nlines with an interlayer capacitance of 7.5 µF cm-2, consistent with theoretical expectations for\nmisaligned twisted bilayer graphene and with previous experimental results (ref. 20). Second,\nthe Raman spectra of the suspended region match those reported for twisted bilayer\ngraphene (Supplementary Fig. 2, ref. 26-28). Note that the spectra do not display hBN bands,\nwhich would apparent if hBN was present. Third, proton transport through the bilayer requires\ndirect graphene–graphene contact and would be impossible if the layers were separated by\nas little as 4 layers of hBN, which are known to block proton flow (ref. 9).\nNevertheless, following the Reviewer comment we have now performed scanning\ntransmission electron microscopy (STEM) analysis of our twisted bilayer graphene samples to\nconfirm contact of the individual graphene layers. Atomic resolution imaging of the sample\nreveals a clear moiré pattern resulting from the direct contact of the individual graphene\nlayers within the bilayer with a measurable interlayer twist angle of 12.5° and a corresponding\nmoiré period of 1.18±0.06 nm. The atomic resolution HAADF STEM image has been\nincorporated in Fig. 1a in the revised manuscript (see also point #1 from Reviewer 3).\n2. The 24-hour state retention under constant gate voltages (Figure 1f) is impressive for\nmemory applications, but the practical implementation requires demonstration of cyclical\nstability. While Raman data in Supplementary Fig. 5b suggests some reversibility, \ncomplementary electronic transport data showing multiple hydrogenation-dehydrogenation\ncycles are lacking. Quantification of performance metrics such as ON/OFF ratio degradation\nover cycles would significantly strengthen the application potential claims.\nFollowing the reviewer comment, we have performed a cyclability test (Supplementary Fig. 6\nin revised manuscript) and discussed the performance metrics in main text and the section\n“Configurable parallel logic gate measurements”. We found that the selective hydrogenation\nprocess is highly reproducible, with >1000 cycles with stable ON/OFF ratio of >104 and less\nthan 6% cycle-to-cycle variation. Such performance is within order of magnitude of promising\nelectronic floating-gate 2D logic-in-memory devices, which achieve >5,000 ON/OFF cycles\n[Nature, 2020, 587(7832): 72-77].\n3. The logic gate demonstration in Figure 3 is conceptually interesting, but lacks quantitative\nperformance benchmarks. Explicit documentation of ON/OFF current ratios for each output\nunder standardized conditions would enable proper evaluation of the logic operation quality.\nAdditionally, characterization of switching speed and cycle-to-cycle variation would provide\ncrucial information for assessing practical applicability.\nFollowing the Reviewer’s comment, we have characterised the ON/OFF current ratios and\ncycle variability under standardised conditions (see also point #2) and now report these\nresults in the Methods section “Configurable parallel logic gate measurements”. In addition,\nwe have performed dedicated measurements of the hydrogenation switching speed, which\nwe reported in a manuscript a couple of months ago (ref. 23 in revised manuscript). Fig. R1\n(adapted from our recent manuscripts) shows that the switching time depends strongly on\nthe applied potential, ranging from seconds at 1.7 V vs\nNP to less than one microsecond. The limiting\nswitching speed is around 10 times the RC time\nconstant of the electrochemical circuit, which arises\nfrom the formation of the electrochemical double\nlayer.\nFig. R1 | Device switching speed based on\nhydrogenation process. Time necessary to achieve the\ninsulating transition as a function of V (left y-axis).\nG\nRight y-axis, corresponding proton adsorption rate.\nTriangle marks the rate of acceleration of the\nswitching speed with gate voltage. Vertical dashed\nline marks the minimum potential required to observe\nthe hydrogenation transition.\n4. While the manuscript highlights the advance beyond previous work on monolayer\ngraphene, the introduction could more precisely articulate the specific conceptual leap\nachieved by the decoupled bilayer architecture. The outlook section would benefit from\nconcrete examples of other 2D heterostructures where this approach could be applied, such\nas twisted transition metal dichalcogenide systems for ion intercalation control.\nFollowing the Reviewer comment we have now articulated the key conceptual leap achieved\nby our devices and the potential of similar structures for other chemical processes, such as\nintercalation in the conclusions/outlook page 6, last paragraph.\nIn brief, in a classical electrode–electrolyte interfaces, interfacial processes arise from\ncontrolling a single electronic system. Here, we introduce a new class of interface formed by\ntwo electronically independent layers, which enables access to regimes that are unavailable\notherwise. Specifically, at fixed carrier density 𝑛 but varying electric field 𝐸 , a succiently\nstrong 𝐸polarises the bilayer and redistributes charge between the layers, driving conductor–\ninsulator transitions. This is in stark contrast to monolayers, where such transitions are\ncontrolled solely by 𝑛 . The presence of these additional control variables introduces new\nreaction pathways for interfacial chemistry and opens opportunities for proton- and ion-based\nlogic and memory architectures. Similar concepts could be extended to other layered systems,\nsuch as TMDC bilayers, where twisting or inserting thin hBN spacers may lead to rich\nintercalation phenomena by controlling independent electronic systems in a 2D\nheterostructure.\nResponse to comment from Reviewer #2\nThe authors report layer-selective protonation in twisted bilayer graphene using double\nelectrolyte gating and further demonstrate configurable logic operations. Independent\ncontrol of the electric field and carrier density is claimed to modulate the resistance of each\nlayer. The results are intriguing, but several aspects of the mechanism and data interpretation\nrequire clarification, as follows:\nWe thank the Reviewer for taking the time to review our manuscript. We have done our best\nto address the points raised.\n1. The authors analyze their data based on an electric field defined as E ∝ Vt - Vb. However,\nthis definition is not physically reasonable in the double electrolyte gating. I suggest analyzing\nthe results in terms of the individual gate voltages (Vt and Vb), both their sign and magnitude,\nfor the following reasons.\nThe electrolyte contains both cations and anions. Under positive bias, H+ ions migrate toward\nthe graphene, while under negative bias, TFSI- or O2- ions move toward the interface. TFSI-\nions induce mainly electrostatic effects, whereas O2- ions can lead to both electrostatic and\nelectrochemical modifications of graphene. Thus, both types of negatively charged species\naffect the conductivity of graphene.\nWhen analyzing Fig. 2 by decomposing the data into Vt and Vb components, both top and\nbottom graphene layers show abrupt conductance decreases at approximately Vt (or Vb) = ~2\nV. This appears to be a critical voltage corresponding to H+ migration into the respective layer.\nTherefore, the electric potential and field should be defined separately for each layer, rather\nthan using a global Vt - Vb term, which is not succiently meaningful to describe layer-specific\nconductance changes.\n2. The assumption that carrier density is simply proportional to Vt + Vb is also not reasonable.\nThis model implicitly assumes that only H+ ions participate in gating. However, when Vt or Vb\nis negative, migration of TFSI- or O2- ions should also be considered. It would therefore be\nmore reasonable to define and evaluate carrier density individually for each layer.\n3. The carrier density is estimated by simple equations, but such estimates are often\ninaccurate for electrolyte gating. Ionic gating typically involves both electrostatic accumulation\nand electrochemical reactions, and electric-double layers are formed on the surface.\nThis means that carrier density cannot be defined solely by applied voltage. I recommend\ndirectly measuring carrier density using Hall measurements or an equivalent experimental approach.\nAs discussed above, the fact that the charge density is set by V + V is an experimental\nt b\nobservation. We then modelled this behaviour using analytical formulas based on the\nmeasured conductivity, which make no assumptions on the ions involved, only on the Debye\nlength of the electrolyte and the solvent dielectric constant. While Hall effect measurements\nwould more precisely determine the carrier density, such precision is not required to support\nthe conclusions of this work. We therefore view these measurements as valuable future\nfollow-up rather than essential to the present study.\n4. The authors attribute independent modulation of the top and bottom layer resistances to\nelectronic decoupling induced by the large twist angle. However, the observed independence\ncould simply result from the independent control of Vt and Vb for each layer, rather than from\nthe twisted structure itself. It remains unclear whether the twist angle plays any essential role.\nI suggest presenting twist-angle-dependent measurements to support this claim.\nThe decoupling induced by the large twist angle is essential to observing independent\nmodulation of the top and bottom layer resistances. This is evident when compared with\nnaturally AB-stacked bilayer graphene, where the layers are strongly hybridised and their\nconductivities cannot be measured separately. In the AB-stacked case the system behaves as\na single electronic unit, and measuring each layer’s conductivity is impossible. While it would\nbe interesting to study the twist angle dependence of the process, such extensive study would\noverload our already extensive manuscript. We therefore view these measurements as\ninteresting future follow-up work.\n5. TFSI-based ionic liquids are known to contain residual water, which allows migration of both\nH+ and O2- ions. Please refer to previous reports showing H+ migration under positive bias\nand O2- migration under negative bias (Nature 2017, 546, 124–128; ACS Nano 2022, 16, 6206–\n6214). H-TFSI systems are also hygroscopic, enabling H+ and O2- migration during gating.\nTherefore, it is highly possible that O2- ions migrate into graphene under negative Vt or Vb.\nThe possibility that other ions besides protons are behind the conductor-insulator transition\nin graphene is ruled out by control experiments in which we used the same solvent and\npreparation methods but exchanged HTFSI for LiTFSI. No conductor-insulator transition nor D\nband is observed in the Raman spectra of the samples for positive potentials (Fig. R2.3a).\nThese data were reported in Supplementary Fig. 4 in ref. 2, and we include it here as Fig. R2.3a.\nMoreover, Fig. R2.3b, shows that when negative gate voltage of -1.2 V is applied with HTFSI,\nno D peak appears, ruling out TFSI- or O - species as the source of our observations.\n2\n6. The manuscript states that the top and bottom graphene layers are in contact within the\naperture of the hBN layer. Please clarify the thickness of the hBN spacer and whether the two\ngraphene layers are indeed in electrical contact. The data in Fig. 2 suggest connection between\nlayers, but the term “tunneling current” used to describe the measurement is confusing. It\nseems more appropriate to describe this simply as out-of-plane current between the two\ngraphene sheets rather than tunneling through a barrier.\nThe hBN spacer away from the gated region is 20 nm thick and within the contact region there\nis no hBN at all. The two graphene layers are in direct electrical contact in the suspended\nregion. Regarding the use of term ‘tunnelling current’, we respectfully point out that because\nelectrons transfer through the vacuum space between the layers, the transport is due to\ntunnelling. For this reason, we have retained this term in the manuscript but have clarified\nthat the layers are indeed in direct contact.\nResponse to comment from Reviewer #3\nThe authors demonstrate hydrogenation and proton transport in twisted bilayer graphene.\nBased on AA stacked region in twisted bilayer by employed hBN spacer with hole, the\nconductance variation of bilayer as a function of electric field of hydrogenation/de-\nhydrogeneration and top, bottom gate voltage (Vt and Vb). Since this manuscript introduces\na layer selective proton transport characterization as well as its logic application of twisted\nbilayer graphene, this result will be a good reference on electrolyte gating graphene research\nfield. However, because the mechanically stacked bilayer graphene leads to various complex\nsurface condition comparing with their previous paper about electrolyte gating study for\nmonolayer graphene (Ref. 2), more detail experimental results and explanations should be\nsupplemented for publication. The detailed comments are as follows.\nWe thank the Reviewer for taking the time to review our manuscript. Below, we present\nadditional characterisation and discussions to address the points realised.\n1. During mechanically stacking of graphene layers, undesired bubbles and wrinkles often\narise and can influence conductance variability and proton transport in stacked bilayer\ngraphene. Because authors analyze AA and AB stacking in twisted bilayer graphene (TBG)\nincluding the associated area fractions and specific twist angles, it is important to distinguish\nintrinsic stacking effects from extrinsic disorder. To address this, please provide additional\nevidence and a deeper explanation demonstrating that the contact/interfacial area of the\ntwisted bilayer is clean and representative. In particular, direct structural characterization\n(e.g., HRTEM) to map AA/AB domains without undesired bubbles and wrinkles would\nsubstantially strengthen the manuscript.\nFollowing the Reviewer’s recommendation, we conducted atomic resolution high angle\nannular dark field (HAADF) STEM imaging of the devices in collaboration with our colleague\nProf. Sarah Haigh. The images show that the devices are free from significant contamination\nand display the expected hexagonal Moiré pattern with the hexagonal distribution of AA and\nAB stacking regions (Fig. R3.1a&b). The new images are included in Fig. 1a in the revised\nmanuscript.\n2. Authors propose that AA-stacked bilayer graphene hydrogenates at a lower charge-density\nthreshold than monolayer graphene (Ref. 2) and attribute this to electric-field differences. For\nclarity, please articulate the discussion of which physical factors most plausibly account for\nthe reduced threshold. Framing the observation within these mechanisms would strengthen\nthe manuscript.\nThis is an important point and goes to the core of our main finding. In the experiments, we\nfixed the total electron charge density in the bilayer at a level too low to trigger hydrogenation\nof the crystal. By increasing the electric field, the system becomes polarised: electrons and\nholes are driven towards opposite graphene layers. As a result, one layer accumulates\nelectrons while the other becomes increasingly hole doped. When the electric field is\nsucciently strong, the electron density in one layer reaches the threshold for hydrogenation,\nwhile the opposite layer is pushed further into p-type doping. Importantly, the total charge in\nthe bilayer remains constant; only its distribution between the two layers changes as a result\nof the polarising electric field.\n3. For finding neutrality line, authors employed calculation with capacitance values extracted\nfrom references. Furthermore, since the Supplementary Fig. 6 exhibits CNP for natural\n(Bernal) stacked bilayer, we can easily observe the single CNP for Bernal (AB) stacked bilayer\ngraphene. However, if there are layer selected conductance variation for top and bottom\ngraphene, we could observe charge neutrality position (CNP) of transport curve for top and\nbottom monolayer graphene as a function of Vt or Vb, respectively. Furthermore, we will\nobserve more mixed CNP behavior dependent on twisted bilayer graphene area. I can also see\nCNP shapes as a function of E for conducting condition of top and bottom layer in Fig. 1 c and\nd. If authors exhibit externally experimental CNP behavior as well as discussion about it, their\nmanuscript will be more strengthened, too.\nWe observed the splitting of the neutrality lines experimentally for our twisted bilayer\ngraphene samples. This is shown in Fig. 2d inset in the main text, where we fitted these data\nwith the theory lines. Fig. R3.3 shows the experimental data without the theory lines, as well\nas cuts from the map, to highlight that the neutrality lines are directly visible. The splitting of\nthe neutrality line is fully consistent with the discussion in point #2. Namely, in the double\ngated configuration, V + V fixes the total charge density of the bilayer, whereas the electric\nt b\nfield polarises the bilayer and thus redistributes charge between the layers. This phenomenon\nis fully accounted for by our analytical theory, which correctly predicts the position of the\nneutrality lines. These data has been added as Supplementary Fig. 9 in the revised manuscript.\n4. There should be mentions for scale bar sizes in Supplementary Fig.2 b, c and Fig. 6 a.\nThank you for noticing this. The scale bar sizes have been added in the revised manuscript.\nResponse to comment from Reviewer #4\nThe manuscript presents an elegant and conceptually innovative study of electrochemical\nhydrogenation and proton transport in twisted bilayer graphene (TBG) under dual ionic gating.\nBuilding on the authors’ recent paper in Nature demonstrating decoupled control of proton\ntransport and hydrogenation in monolayer graphene, this work extends the paradigm to\ntwisted bilayers, exploiting twist-induced electronic decoupling to achieve layer-selective\nhydrogenation and logic operations within a single device. This represents a significant\nadvance: by leveraging the independent carrier densities emerging from the two-layer\nelectronic systems of large-angle TBG, the authors introduce a new type of electrode–\nelectrolyte interface in which electrochemical processes can be spatially and electronically\npartitioned at room temperature. The demonstration of configurable NOT, NOR, NAND, and\nXOR logic elements—arising from a single material platform and controlled solely via gate\nvoltages—is very nice, and opens promising avenues for ion–electron hybrid information\nprocessing.\nThe experimental methodology is sound, and the characterization (conductance mapping,\ntunneling measurements, Raman spectroscopy, and DFT calculations) provides a largely\ncoherent picture of the underlying processes. The work is also clearly novel relative to the\ngroup’s earlier monolayer study: the ability to target hydrogenation to an individual graphene\nlayer at fixed overall charge density, and to use this selectivity as a functional device degree\nof freedom, is new, nontrivial, and likely to be of broad interest to the community.\nThat said, two aspects of the study would benefit from further clarification and tempering of\nclaims.\nWe are grateful for this encouraging evaluation of our manuscript and for the fair and focused\nreview of our results.\n1. Lack of systematic controls on untwisted (AB-stacked) bilayer graphene.\nThe manuscript includes only a minimal control measurement on AB-stacked bilayers—\nnamely, a conductance map showing a single neutrality line. While this does verify the\nexpected absence of layer decoupling, it does not test whether hydrogenation, proton\ntransport, or logic functionality differ qualitatively from the twisted case. Because the main\nclaims rely on the emergence of layer-selective behavior due to twist-induced electronic\nisolation, a more complete comparison with untwisted bilayers would significantly strengthen\nthe conclusions. Even basic measurements—such as whether AB bilayers undergo single-layer\nor simultaneous dual-layer hydrogenation under equivalent fields, or whether proton\ntransport is observable at all—would help establish that the observed phenomena are\nuniquely rooted in twist-angle physics rather than more general features of bilayer graphene\nunder high electric fields.\nWe agree with the Reviewer’s comment. In the revised manuscript, we have now included the\nrequested control measurements on AB-stacked bilayers. As expected, the behaviour of AB\nbilayers is qualitatively different from that of twisted bilayers.\nFirst, natural AB bilayers are impermeable to protons, even under large fields. We\ndemonstrated this in our previous work (ref. 2, Fig. 1b), and we now include equivalent\nmeasurements in the revised manuscript (Supplementary Fig. 7e), confirming the absence of\nproton transport in AB bilayers. Second, because the two graphene layers in AB stacking are\nelectronically coupled, it is not possible to induce layer-selective conductor–insulator\ntransitions. When a succiently large potential is applied to one side, the upper surface of the\nbilayer can be hydrogenated, which is reflected by a conductance drop at the corresponding\npotential (Supplementary Fig. 7c). However, the bilayer remains overall conductive. Only when\na large potential is subsequently applied to the opposite side, does the system undergo a full\ninsulating transition (Supplementary Fig. 7d). These control measurements show that twist-\ninduced electronic decoupling is essential for enabling both layer-selective hydrogenation and\nlogic functionality.\n2. Interpretation of the AA-stacked regions as the exclusive proton-transport pathway.\nThe manuscript repeatedly attributes proton permeation primarily to AA regions of the Moiré\nsuperlattice. Although this interpretation is physically plausible and supported by DFT barrier\ncalculations, it remains hypothetical within the context of the experimental data presented.\nThe proton-current measurements are spatially unresolved, and no experiment directly\nevidences transport localization to AA regions or correlates permeation with twist-angle-\ndependent AA area fraction. I recommend that the authors moderate the certainty of these\nclaims and clarify that the AA contribution, while consistent with theoretical expectations, is\nnot experimentally demonstrated. Future work—such as twist-angle dependence studies,\nspatially patterned gating, or correlated imaging—could substantiate this point.\nWe agree with the Reviewer. We have moderated this claim in the abstract and main text.\nIn summary, this is a strong manuscript that presents noteworthy advances in electrochemical\ncontrol of two-dimensional heterostructures. With a modest softening of the AA-region\ninterpretation and consideration of additional bilayer-control measurements, the paper will\nprovide a clearer and more rigorously supported account of an important new\nelectrochemical phenomenon in twisted bilayer graphene. I find the work to be of high quality\nand recommend publication after these points are addressed.\nWe are truly grateful to the Reviewer for their strong support of our work."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have provided a comprehensive and persuasive response to the initial review, significantly strengthening the\nmanuscript through additional experiments, characterization, and discussion. This study remains a highly compelling\ndemonstration of a novel electrode-electrolyte interface concept using twisted bilayer graphene. All major concerns raised\nhave been effectively addressed:\n1. The crucial question regarding the coherent bilayer nature of the interface has been conclusively resolved with the\naddition of atomic-resolution STEM imaging, which directly reveals the moiré pattern. This evidence, combined with the\nexisting transport, Raman, and proton-blocking data, solidly validates the twisted bilayer system.\n2. The practical applicability of the memory function is now strongly supported by the new cyclability data showing >1000\nreproducible hydrogenation-dehydrogenation cycles with stable performance, moving beyond the initial impressive state\nretention.\n3. The logic gate demonstrations are now underpinned by quantitative performance benchmarks, including ON/OFF ratios\nand cycle variability under standardized conditions. The discussion of switching speed, supported by prior work, adds\ncrucial context for assessing potential applications.\n4. The manuscript now more precisely articulates the conceptual leap enabled by the decoupled bilayer architecture and\nprovides a concrete outlook on extending this approach to other 2D heterostructures.", "reviewer_2": "The authors have revised the manuscript and addressed most of the reviewer comments. However, the key claims of the\nmanuscript are still not supported by sufficient experimental evidence, and therefore I cannot recommend publication of the\ncurrent version.\nThe thickness of the hBN spacer is only 20 nm, while the width of the hBN aperture appears to be on the order of ~10 μm.\nUnder this geometry, it is highly plausible that the top and bottom graphene layers come into physical contact at the center of\nthe aperture. If such physical contact occurs, the electron transport between the top and bottom graphene layers should not\nbe described as tunneling current. Therefore, the authors must provide direct experimental evidence demonstrating that the\ntop and bottom graphene layers are not in physical contact within the aperture region. Otherwise, the use of the term\n“tunneling current” is not justified and should be avoided throughout the manuscript.", "reviewer_3": "The authors have adequately addressed the reviewers’ concerns. Therefore, I recommend this manuscript for publication in\nNature Communications.", "reviewer_4": "The response to referees is substantive, and I think the manuscript is acceptable for publication."}, "author_response": "Response to comments from Reviewer #1\nThe authors have provided a comprehensive and persuasive response to the initial review, significantly\nstrengthening the manuscript through additional experiments, characterization, and discussion. This\nstudy remains a highly compelling demonstration of a novel electrode-electrolyte interface concept\nusing twisted bilayer graphene. All major concerns raised have been effectively addressed:\n1. The crucial question regarding the coherent bilayer nature of the interface has been conclusively\nresolved with the addition of atomic-resolution STEM imaging, which directly reveals the moiré pattern.\nThis evidence, combined with the existing transport, Raman, and proton-blocking data, solidly validates\nthe twisted bilayer system.\n2. The practical applicability of the memory function is now strongly supported by the new cyclability data\nshowing >1000 reproducible hydrogenation-dehydrogenation cycles with stable performance, moving\nbeyond the initial impressive state retention.\n3. The logic gate demonstrations are now underpinned by quantitative performance benchmarks,\nincluding ON/OFF ratios and cycle variability under standardized conditions. The discussion of switching\nspeed, supported by prior work, adds crucial context for assessing potential applications.\n4. The manuscript now more precisely articulates the conceptual leap enabled by the decoupled bilayer\narchitecture and provides a concrete outlook on extending this approach to other 2D heterostructures.\nWe thank the Reviewer for their support of our work.\nResponse to comments from Reviewer #2\nThe authors have revised the manuscript and addressed most of the reviewer comments. However, the\nkey claims of the manuscript are still not supported by sufficient experimental evidence, and therefore I\ncannot recommend publication of the current version.\nThe thickness of the hBN spacer is only 20 nm, while the width of the hBN aperture appears to be on the\norder of ~10 μm. Under this geometry, it is highly plausible that the top and bottom graphene layers come\ninto physical contact at the center of the aperture. If such physical contact occurs, the electron transport\nbetween the top and bottom graphene layers should not be described as tunneling current. Therefore,\nthe authors must provide direct experimental evidence demonstrating that the top and bottom graphene\nlayers are not in physical contact within the aperture region. Otherwise, the use of the term “tunneling\ncurrent” is not justified and should be avoided throughout the manuscript.\nWe believe there is a misunderstanding. The top and bottom graphene layers are intentionally in direct\ncontact across the entire aperture, as the hBN spacer is fully etched in this region. This is essential for\ndevice operation. Although the layers are in physical contact, they are electronically decoupled due to\nthe large twist angle. As a result, charge transport across the aperture occurs via electron tunnelling\nacross the interlayer vacuum gap between the two graphene sheets, rather than through hBN. Describing\nthis process as tunnelling is established in the literature for twisted graphene systems. See, for example,\nP. Rickhaus et al., Sci. Adv. 2020, 6, eaay8409. science.org/doi/10.1126/sciadv.aay8409; A. Mrenca-\nKolasinska et al., 2D Mater. 2022, 9, 025013. iopscience.iop.org/article/10.1088/2053-1583/ac5536.\nResponse to comments from Reviewer #3\nThe authors have adequately addressed the reviewers’ concerns. Therefore, I recommend this\nmanuscript for publication in Nature Communications.\nWe are grateful to the Reviewer for this recommendation.\nResponse to comments from Reviewer #4\nThe response to referees is substantive, and I think the manuscript is acceptable for publication.\nWe thank the Reviewer for their support of our manuscript."}, {"round": 3, "reviewer_comments": {"reviewer_1": "After carefully examining the persistive technical issues, I agree with the authors’ adoption of quantum tunneling to explain\nthe electron transport across the vdW gaps between two fully electronically decoupled graphene. Although lack direction\nevidence in this study, the concept is in line with recent understanding of decoupled graphene with sufficient spatial\nseparation of the Dirac cones. Further verification of the transport nature, although interesting, is clearly beyond the scope of\nthis work.\nOverall, I believe that the author has established a novel maneuverability of hydrogenation and proton transport in bilayer\ngraphene system, and more importantly its practical implications in function devices. This work can be published at its\ncurrent form.\nIn addtion, i do suggestion a clearer presentation of the key concept,device structure and fabrication, as the paper itself\nmaybe challenging to read for broader audiences."}, "author_response": ""}]

Decision letter