## 1 Introduction  
Plasma technologies using a wide scale of plasma working gases has succeeded as a powerful tool for surface cleaning, functionalization, adhesion improvement, deposition, sputtering and etching. Hydrogen plasma is a very strong reducing agent already tested for the surface treatments of metals, silicon, carbon, and polymer materials. A comprehensive summary of plasma etching of polymers and polymeric materials including the hydrogen plasma etching can be found in the review of [PERSON] and [PERSON] [1]. In general, when polymer surfaces are exposed to the hydrogen plasma, the bombardment by plasma species (electrons, hydrogen ions and radicals) led to the degradation of the surface and etching reactions will occur. The effect of hydrogen content in low-pressure N\({}_{2}\)/H\({}_{2}\) plasma for surface modification of polyethylene (PE), poly(tetrafluoroethylene) (PTFE) and polyvinylidene fluoride (PVDF) studied [PERSON] et al. [2]. Hydrogen-containing plasma was found to causing dehydrohalogenation along the fluoropolymerbackbone [3]. Subsequently, the co-process gas can covalently attach to these sites; thus, the hydrogen plasma with a co-process gas can particularly improve the adhesive bonds of fluoropolymers. Selective removal of polymeric PMMA residues on monolayer graphene by high-density, low pressure H\({}_{2}\) and H\({}_{2}\)/N\({}_{2}\) plasmas without a damage to the graphene surface as examined by [PERSON] et al. [4]. Selective etching of graphene edges and graphene nanoribbons using hydrogen plasma reaction at 300 \({}^{\circ}\)C and at a pressure of 300 mTorr was studied by [PERSON] et al. [5]. The advantage of selective plasma etching using hydrogen as etchant gas was used for selective preparation of metallic and semiconducting single-wall carbon nanotubes by [PERSON] et al. [6] and [PERSON] et al. [7]. Inline plasma surface treatments showed a significant potential for applications in high volume and cost-effective roll-to-roll (R2R) fabrication of flexible electronics on a polymer web substrate including, for example, flexible solar cell and wearable electronics fabrication. Virtually all these applications need diffuse non-thermal plasma. We use the wording \"diffuse plasma\" in accordance with the term published for the first time by [PERSON] et al. in 2002 [8]. The \"diffusivity\" of the plasma is related to the visual uniformity of the generated plasma as observed by the human eye. So that we used the term diffuse plasma to refer to the plasma which, when visually observed, is widely spread, and not concentrated to individual plasma filaments. In our experience, the diffuse, visually uniform plasma enables uniform plasma surface modification working at the plasma exposure times longer than the time resolution of a human eye. However, such plasma generated at low pressure in costly vacuum systems is at odds with high throughput processing required in industry [9]. However, the developments in the field of plasma physics during the last two decades have opened a way how to generate stable, diffuse and non-thermal plasma at atmospheric pressure [10]. The research of atmospheric plasma, including the atmospheric-pressure H\({}_{2}\) plasma, has been driven by the need of replacing of expensive vacuum systems by simpler, more cost-effective and high-throughput systems [9]. For example, [11] studied plasma etching of various polymers like PP, PET, PEN, PEEK, PMMA, PLA, LDPE and Nylon 6.6 using atmospheric pressure hydrogen plasma. [PERSON] et al. [12] used hydrogen plasma sintering process at temperature 150 \({}^{\circ}\)C for reduction and densification of copper complex ink on flexible PET substrate. The so-called Diffuse Coplanar Surface Barrier Discharge (DCSBD) is capable to generate visually an almost uniform diffuse ambient air plasma with effective thickness of approximately 0.25 mm [13].