После работы мне труднее сосредоточиться, чем утром.

Because после requires the genitive case.

• работа = nominative singular
• работы = genitive singular

So:

• после работы = after work

This is a very common pattern in Russian:

• после урока = after the lesson
• после обеда = after lunch
• после фильма = after the film

So the case here is determined by the preposition после.

Russian often expresses experiences like it is hard/easy for me, I feel cold, I am sorry, etc. with the dative case, not the nominative.

So:

• мне трудно = it is difficult for me
• мне легче = it is easier for me
• мне холодно = I am cold

In this sentence, мне труднее сосредоточиться literally means something like:

• To me, it is harder to concentrate

Natural English translates this as I find it harder to concentrate or simply It’s harder for me to concentrate.

So мне is not a direct translation of I. It is part of a common Russian structure.

Труднее is the comparative form of трудно.

• трудно = difficult, hard
• труднее = more difficult, harder

So:

• мне трудно сосредоточиться = it is hard for me to concentrate
• мне труднее сосредоточиться = it is harder for me to concentrate

Russian often uses these short comparative forms instead of adding a separate word like more.

Other examples:

• легко → легче = easy → easier
• плохо → хуже = bad → worse
• хорошо → лучше = well/good → better

Сосредоточиться is the infinitive to concentrate / to focus.

The -ся ending marks it as a reflexive verb. In many cases, reflexive verbs in Russian do not mean literal self-action in the English sense; they are just the normal dictionary form for that meaning.

Here:

• сосредоточить = to concentrate something, to direct/focus something
• сосредоточиться = to concentrate, to focus oneself / become focused

In this sentence, you need the intransitive meaning to concentrate, so сосредоточиться is the correct choice.

Because the structure is:

• мне труднее + infinitive

This means it is harder for me to do something.

So:

• мне трудно читать = it is hard for me to read
• мне легко говорить по-русски = it is easy for me to speak Russian
• мне труднее сосредоточиться = it is harder for me to concentrate

Russian often uses this pattern where English might also use an infinitive.

Чем is used to introduce the second part of a comparison, like than in English.

So:

• труднее ..., чем ... = harder ..., than ...

In this sentence:

• После работы мне труднее сосредоточиться, чем утром.
• After work, it’s harder for me to concentrate than in the morning.

Other examples:

• Он выше, чем я. = He is taller than I am / than me.
• Сегодня холоднее, чем вчера. = Today is colder than yesterday.

Because in Russian, comparisons with чем are typically separated by a comma.

So:

• труднее сосредоточиться, чем утром

This is standard punctuation in Russian.

Even though English often does not always make this pause obvious, Russian normally writes it with a comma.

Утром is the instrumental case form of утро, and Russian very often uses time expressions in the instrumental without a preposition.

So:

• утром = in the morning
• днём = in the daytime / during the day
• вечером = in the evening
• ночью = at night

This is just a common time-expression pattern.

So the comparison is:

• after work
• than in the morning

Russian expresses that second part simply as чем утром.

In most contexts, после работы naturally means after work or after work is over.

It usually refers to the time after someone finishes their job for the day, not necessarily after the work in a very specific grammatical sense.

So in everyday speech:

• После работы я иду домой. = After work I go home.
• После работы мне труднее сосредоточиться. = After work it’s harder for me to concentrate.

English often drops the article here too, and Russian does not use articles anyway.

Russian often omits the equivalent of it is in sentences like this.

English says:

• It is harder for me to concentrate

Russian simply says:

• Мне труднее сосредоточиться

This is a normal impersonal structure. Russian does not need a dummy subject like English it.

So the sentence is complete without any extra verb.

Yes. Russian word order is flexible, although the original order sounds very natural.

Original:

• После работы мне труднее сосредоточиться, чем утром.

You could also hear:

• Мне труднее сосредоточиться после работы, чем утром.
• Сосредоточиться после работы мне труднее, чем утром.

These versions shift emphasis slightly:

• После работы first puts focus on the time
• мне early can emphasize the experiencer
• сосредоточиться first can emphasize the action itself

But the original sentence is the most neutral and natural way to say it.

Both can be possible in some contexts, but труднее sounds more natural here.

• трудно / труднее = hard, difficult, requiring effort
• сложно / сложнее = difficult, complicated, complex

Concentrating after work is usually hard because of tiredness, effort, or mental state, so труднее fits well.

If you said сложнее сосредоточиться, it would not be wrong, but it may sound a little less natural in this everyday context. Труднее is the more idiomatic choice here.